feat(#74): IMP-45 u1~u8 slide-level CSS override (frontmatter slide_overrides.css + --override-slide-css/--slide-css-file + idempotent Step 13 injector)

u1 KNOWN_AXES tuple gains slide_css entry in src/user_overrides_io.py (snake_case parity with image_overrides); round-trip test extends to 6 axes. u2 src/mdx_normalizer.py surfaces nested slide_overrides.css from the MDX frontmatter into the normalize_mdx_content return dict; absent key -> {}, non-string css drops. 4 unit cases in tests/test_mdx_normalizer.py (present / absent / non-string / title-only). u3 src/slide_css_injector.py NEW (88 lines) mirrors the inject_image_overrides_style contract from src/image_id_stamper.py: marker pair  / , idempotent re-injection, </head> > <body> > document-start three-tier fallback, empty/None -> unchanged. 8 fixtures in tests/test_slide_css_injector.py mirror test_image_id_stamper.py. u4 run_phase_z2_mvp1 accepts override_slide_css: Optional[str] = None; None -> frontmatter slide_overrides.css fallback. Step 13 calls inject_slide_css after image override injection and before the final.html disk write, so CLI/CI/regression renders observe the same backend artifact. u5 argparse adds mutually-exclusive --override-slide-css TEXT (inline CSS, <style> wrapper optional) and --slide-css-file PATH (UTF-8 read, fail-closed sys.exit(2) on missing path / decode error / both flags present). Resolved string is forwarded as override_slide_css kwarg. 6 cases in tests/test_phase_z2_cli_overrides.py (inline / file / both / missing / non-utf8 / neither). u6 samples/mdx_batch/04.mdx frontmatter gains slide_overrides.css block (verbatim of the former MDX04_DEFAULT_OVERRIDE_CSS constant, no sample/frame gate). Subprocess smoke in tests/test_phase_z2_slide_css_smoke.py verifies the marker pair and CSS substring land in final.html. u7 Front/client removes the sample/frame-gated frontend-only injection: Home.tsx drops the MDX04_DEFAULT_OVERRIDE_CSS constant and the sample==="04"+frame==="process_product_two_way" branch (-28 lines); SlideCanvas.tsx drops the iframe contentDocument.head injection of that prop (-14 lines). Live preview now reads backend final.html only. u8 tests/regression/fixtures/89a_pre_baseline_sha.json 04.mdx entry resyncs to the live SHA ddb6bf2f... / 28042 bytes (overwrites the earlier 5-byte-drift d02c76fd... / 28047). Other entries untouched. Note: 01.mdx baseline drift (ad6f16a3... / 29089 -> live f26a7fac... / 29084) predates this branch and is split to a follow-up issue per the closed-issue fresh validation rule. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
2026-05-25 03:26:03 +09:00
parent b4be6c1cd0
commit 9062931863
14 changed files with 740 additions and 55 deletions
--- a/Front/client/src/components/SlideCanvas.tsx
+++ b/Front/client/src/components/SlideCanvas.tsx
@@ -36,10 +36,6 @@ interface SlideCanvasProps {
  userSelection: UserSelection;
  /** Phase Z 가 만든 final.html URL (iframe 으로 표시). */
  finalHtmlUrl?: string;
-  /** 슬라이드 단위 inline CSS override (catalog/template 무변, iframe contentDocument 에
-   *  동적 inject). Home 이 mdx 별 default visual 보완 등을 지정. 빈 문자열/undefined =
-   *  inject 안 함. 사용자 lock 2026-05-14 — slide-level only. */
-  slideOverrideCss?: string;
  /** 파이프라인 실행 중 표시 (loading state). */
  isPipelineRunning?: boolean;
  /** Phase 2 : pending layout 모드 — final.html iframe 숨기고 빈 layout zone 만 표시. */
@@ -86,7 +82,6 @@ export default function SlideCanvas({
  slidePlan,
  userSelection,
  finalHtmlUrl,
-  slideOverrideCss,
  isPipelineRunning,
  isPendingLayout,
  pendingLayoutId,
@@ -391,15 +386,6 @@ export default function SlideCanvas({
                  const doc = (e.currentTarget as HTMLIFrameElement).contentDocument;
                  if (!doc) return;

-                  // 2026-05-14 — slide-level override CSS (catalog/template 무변).
-                  // Home 이 mdx 별 default visual 보완 (bullet 간격 / zone 비율 등) 지정.
-                  if (slideOverrideCss && slideOverrideCss.trim()) {
-                    const overrideStyle = doc.createElement("style");
-                    overrideStyle.setAttribute("data-purpose", "slide-level-override");
-                    overrideStyle.textContent = slideOverrideCss;
-                    doc.head.appendChild(overrideStyle);
-                  }
-
                  // ── Zone DOM 측정 ──
                  // backend final.html 의 .zone[data-zone-position="..."] 요소를
                  // 찾아서 boundingClientRect 측정 → 1280×720 기준 정규화.
--- a/Front/client/src/pages/Home.tsx
+++ b/Front/client/src/pages/Home.tsx
@@ -242,22 +242,6 @@ export default function Home() {
  // 호출되는 단일 callback. handleFileUpload 가 자동 분석 trigger.
  const [selectedSample, setSelectedSample] = useState<"03" | "04" | "05" | null>(null);

-  // 2026-05-14 — mdx 별 slide-level CSS override (catalog/template 무변, frontend layer only).
-  // SlideCanvas 의 iframe onLoad 에서 동적 inject. 사용자 룰 : "보고용 슬라이드 결과물 단위"
-  // 변경. mdx04 의 default (rank 1 = process_product_two_way) 일 때만 적용 — 사용자 frame
-  // override 후 (rank 2 = bim_dx_comparison_table 등) 다른 frame 시 무적용.
-  const MDX04_DEFAULT_OVERRIDE_CSS = `
-    .slide-body {
-      grid-template-rows: 0.38fr 0.60fr !important;
-      gap: 1.5% !important;
-    }
-    .f29b__cell .text-line + .text-line { margin-top: 1px !important; }
-    .f29b__cell:nth-child(n+3) {
-      padding-top: 3px !important;
-      margin-top: 2px !important;
-    }
-  `.trim();
-
  const handleSelectSample = useCallback(async (which: "03" | "04" | "05") => {
    try {
      const res = await fetch(`/api/sample-mdx?mdx=${encodeURIComponent(which)}`);
@@ -634,17 +618,6 @@ export default function Home() {
    return state.slidePlan;
  }, [pendingZones, state.slidePlan, pendingLayout]);

-  // 2026-05-14 — slide-level CSS override 계산. mdx04 default (rank 1 = process_product_two_way)
-  // 일 때만 적용 (catalog 무변, slide 결과물에만 inject). 사용자 frame override 후 다른
-  // frame 시 무적용 (rank 2 의 frame visual 유지).
-  const slideOverrideCss = useMemo<string | undefined>(() => {
-    if (selectedSample !== "04") return undefined;
-    const zone04_2 = state.slidePlan?.zones.find((z) => z.zone_id === "bottom");
-    const frameId = zone04_2?.internal_regions[0]?.frame_match_strategy.frame_id;
-    if (frameId !== "process_product_two_way") return undefined;
-    return MDX04_DEFAULT_OVERRIDE_CSS;
-  }, [selectedSample, state.slidePlan]);
-
  // ── Frame 선택 ──
  const handleFrameSelect = useCallback((frameId: string) => {
    const zone = getSelectedZone(effectiveSlidePlan, state.userSelection);
@@ -805,7 +778,6 @@ export default function Home() {
            normalizedContent={state.normalizedContent}
            userSelection={state.userSelection}
            finalHtmlUrl={runMeta?.final_html_url}
-            slideOverrideCss={slideOverrideCss}
            isPipelineRunning={state.isLoading}
            isPendingLayout={!!pendingLayout}
            pendingLayoutId={pendingLayout}
--- a/samples/mdx_batch/04.mdx
+++ b/samples/mdx_batch/04.mdx
@@ -2,6 +2,17 @@
 title: DX 지연 요인
 sidebar:
  order: 03
+slide_overrides:
+  css: |
+    .slide-body {
+      grid-template-rows: 0.38fr 0.60fr !important;
+      gap: 1.5% !important;
+    }
+    .f29b__cell .text-line + .text-line { margin-top: 1px !important; }
+    .f29b__cell:nth-child(n+3) {
+      padding-top: 3px !important;
+      margin-top: 2px !important;
+    }
 ---

 ## 1. DX에 대한 인식
--- a/src/mdx_normalizer.py
+++ b/src/mdx_normalizer.py
@@ -392,6 +392,32 @@ def _clean_text(text: str) -> str:
 # 메인 함수
 # ══════════════════════════════════════

+def _extract_slide_overrides(metadata: dict[str, Any]) -> dict[str, Any]:
+    """Surface the nested ``slide_overrides`` mapping from frontmatter.
+
+    IMP-45 (#74) u2 — slide-level CSS override axis intake. Returns a
+    plain ``dict`` so callers (Step 13 injector) can read
+    ``slide_overrides.get("css")`` without re-parsing frontmatter.
+
+    Rules:
+    - Absent or non-mapping → ``{}``.
+    - Inside the mapping, ``css`` is kept only when it is a ``str``
+      (non-string values dropped to fail-closed against typo'd YAML
+      shapes such as ``css: [".x{}"]``).
+    - Unknown sibling keys (e.g., future ``slide_overrides.js``) are
+      preserved verbatim — generalization deferred per Stage 2 scope.
+    """
+    raw = metadata.get("slide_overrides")
+    if not isinstance(raw, dict):
+        return {}
+    out: dict[str, Any] = {}
+    for k, v in raw.items():
+        if k == "css" and not isinstance(v, str):
+            continue
+        out[k] = v
+    return out
+
+
 def normalize_mdx_content(raw_mdx: str) -> dict[str, Any]:
    """MDX 원본을 4-Layer 파서로 정규화.

@@ -405,11 +431,13 @@ def normalize_mdx_content(raw_mdx: str) -> dict[str, Any]:
            "popups": [{"title": str, "content": str}],
            "tables": [{"headers": list, "rows": list}],
            "sections": [{"level": int, "title": str, "content": str}],
+            "slide_overrides": {"css": str, ...} | {},
        }
    """
    # ── Layer 1: frontmatter 분리 ──
    metadata, body = frontmatter.parse(raw_mdx)
    title = metadata.get("title", "")
+    slide_overrides = _extract_slide_overrides(metadata)
    logger.info(f"[Layer 1] title='{title}', metadata keys={list(metadata.keys())}")

    # ── Layer 2: 코드블록 보호 → MDX 패턴 처리 ──
@@ -437,6 +465,7 @@ def normalize_mdx_content(raw_mdx: str) -> dict[str, Any]:
        "popups": popups,
        "tables": tables,
        "sections": sections,
+        "slide_overrides": slide_overrides,
    }


--- a/src/phase_z2_pipeline.py
+++ b/src/phase_z2_pipeline.py
@@ -4843,6 +4843,42 @@ def _run_step0_ai_preflight() -> dict:
    }


+def _resolve_slide_css_from_frontmatter(mdx_source_text: str) -> Optional[str]:
+    """IMP-45 (#74) u4 — minimal frontmatter probe for ``slide_overrides.css``.
+
+    Targeted re-parse of the same YAML frontmatter block that
+    :func:`parse_mdx` reads at line 415-418 — extracts only the
+    nested ``slide_overrides.css`` string when present. Kept inline
+    rather than routed through :func:`src.mdx_normalizer.normalize_mdx_content`
+    so Step 13 render does not depend on the Stage 0 normalize adapter
+    (project lock 2026-05-08).
+
+    Mirrors the validation rules in
+    :func:`src.mdx_normalizer._extract_slide_overrides` (u2) :
+
+    - No frontmatter / unparseable YAML / non-mapping → ``None``.
+    - Missing ``slide_overrides`` mapping → ``None``.
+    - ``slide_overrides.css`` non-string or empty → ``None``.
+    - ``slide_overrides.css`` non-empty ``str`` → that string.
+    """
+    fm_match = re.match(r"^---\n(.*?)\n---\n", mdx_source_text, re.DOTALL)
+    if fm_match is None:
+        return None
+    try:
+        fm = yaml.safe_load(fm_match.group(1))
+    except yaml.YAMLError:
+        return None
+    if not isinstance(fm, dict):
+        return None
+    overrides = fm.get("slide_overrides")
+    if not isinstance(overrides, dict):
+        return None
+    css = overrides.get("css")
+    if isinstance(css, str) and css:
+        return css
+    return None
+
+
 def run_phase_z2_mvp1(
    mdx_path: Path,
    run_id: Optional[str] = None,
@@ -4852,6 +4888,7 @@ def run_phase_z2_mvp1(
    override_zone_geometries: Optional[dict[str, dict]] = None,
    override_section_assignments: Optional[dict[str, list[str]]] = None,
    override_image_overrides: Optional[dict[str, dict]] = None,
+    override_slide_css: Optional[str] = None,
    reuse_from: Optional[str] = None,
 ) -> Path:
    """MVP-1.5b entry — single slide + composition planner v0 + 8 preset vocabulary.
@@ -4875,6 +4912,16 @@ def run_phase_z2_mvp1(
                        backend contract (KNOWN_AXES u1 + Vite allowlist u2 + typed
                        client u3 + stamper u4) end-to-end addressable from CLI without
                        diverging the function signature.
+      override_slide_css : Optional slide-level CSS string — IMP-45 (#74) u4 axis.
+                        Marker-wrapped <style> block injected into ``final.html``
+                        at Step 13 via :func:`src.slide_css_injector.inject_slide_css`
+                        (mirrors the image_id_stamper injection contract). When
+                        ``None``, the MDX frontmatter ``slide_overrides.css`` value
+                        is used as fallback via
+                        :func:`_resolve_slide_css_from_frontmatter`. Kwarg always
+                        wins over frontmatter when provided. The CLI surface
+                        (``--override-slide-css`` inline + ``--slide-css-file``
+                        PATH) lands in u5.

    Incremental rerun (IMP-43 #72, u5) :
      reuse_from : Optional PREV_RUN_ID. When set, Steps 0/1/2/5/6 artifacts
@@ -7191,6 +7238,18 @@ def run_phase_z2_mvp1(
        if _image_overrides_css:
            html = inject_image_overrides_style(html, _image_overrides_css)

+    # IMP-45 (#74) u4 — slide-level CSS override injection.
+    # Kwarg wins; otherwise fall back to MDX frontmatter
+    # ``slide_overrides.css``. Called AFTER image override injection so
+    # editor-authored slide CSS wins ties at the same specificity in the
+    # cascade (slide_css_injector.py module docstring lock).
+    _effective_slide_css = override_slide_css
+    if _effective_slide_css is None:
+        _effective_slide_css = _resolve_slide_css_from_frontmatter(mdx_source_text)
+    if _effective_slide_css:
+        from src.slide_css_injector import inject_slide_css
+        html = inject_slide_css(html, _effective_slide_css)
+
    # 8. Write final.html
    out_path = run_dir / "final.html"
    out_path.write_text(html, encoding="utf-8")
@@ -7903,6 +7962,44 @@ if __name__ == "__main__":
            "--override-image img-def=50,15,40,40"
        ),
    )
+    # IMP-45 (#74) u5 — slide-level CSS override CLI surface. Two mutually
+    # exclusive flags carrying the same axis: ``--override-slide-css TEXT``
+    # passes inline CSS verbatim; ``--slide-css-file PATH`` reads UTF-8
+    # CSS from disk. Both forward into the single ``override_slide_css``
+    # kwarg on :func:`run_phase_z2_mvp1` (u4), which already mirrors the
+    # marker-wrapped image_id_stamper injection contract at Step 13.
+    # Manual mutual-exclusion (not ``add_mutually_exclusive_group``) so the
+    # error stderr can name the axis pair explicitly with ``sys.exit(2)``,
+    # matching sibling override surfaces (--override-frame /
+    # --override-zone-geometry / --override-image).
+    parser.add_argument(
+        "--override-slide-css",
+        dest="override_slide_css",
+        default=None,
+        metavar="CSS_TEXT",
+        help=(
+            "slide-level CSS override (inline). value is passed verbatim "
+            "to the run_phase_z2_mvp1 override_slide_css kwarg; an "
+            "optional outer `<style>` wrapper is allowed because the "
+            "injector wraps the payload in its own marker-bracketed "
+            "`<style>` block regardless. mutually exclusive with "
+            "--slide-css-file."
+        ),
+    )
+    parser.add_argument(
+        "--slide-css-file",
+        dest="slide_css_file",
+        default=None,
+        type=Path,
+        metavar="PATH",
+        help=(
+            "slide-level CSS override (file). UTF-8-encoded CSS payload "
+            "read from PATH and forwarded to the override_slide_css "
+            "kwarg. fail-closed: missing file / non-UTF-8 bytes exit 2 "
+            "with stderr message. mutually exclusive with "
+            "--override-slide-css."
+        ),
+    )
    # IMP-46 u5 — auto-cache opt-in. When set, ``cache.save_proposal``
    # bypasses the ``user_approved`` gate only (``visual_check_passed``
    # is never bypassable). Source of truth is
@@ -8072,6 +8169,40 @@ if __name__ == "__main__":
            sys.exit(2)
        overrides_images[iid] = {"x": x, "y": y, "w": w, "h": h}

+    # IMP-45 (#74) u5 — resolve slide-level CSS override CLI surface to a
+    # single string. Mutually exclusive: both flags set → exit 2. File
+    # path read is UTF-8 strict; missing path or non-UTF-8 bytes → exit
+    # 2. When neither flag is set, ``override_slide_css`` stays ``None``
+    # and Step 13 falls back to the MDX ``slide_overrides.css``
+    # frontmatter via ``_resolve_slide_css_from_frontmatter`` (u4).
+    if args.override_slide_css is not None and args.slide_css_file is not None:
+        print(
+            "[error] --override-slide-css and --slide-css-file are mutually "
+            "exclusive; pass only one.",
+            file=sys.stderr,
+        )
+        sys.exit(2)
+    _final_override_slide_css: Optional[str] = args.override_slide_css
+    if args.slide_css_file is not None:
+        try:
+            _final_override_slide_css = args.slide_css_file.read_text(
+                encoding="utf-8"
+            )
+        except FileNotFoundError:
+            print(
+                f"[error] --slide-css-file path does not exist: "
+                f"{args.slide_css_file}",
+                file=sys.stderr,
+            )
+            sys.exit(2)
+        except UnicodeDecodeError as _exc:
+            print(
+                f"[error] --slide-css-file must be UTF-8 encoded "
+                f"({args.slide_css_file}): {_exc}",
+                file=sys.stderr,
+            )
+            sys.exit(2)
+
    # IMP-52 (#80) u2 — user_overrides.json persistence fallback.
    # After argparse fully parses CLI flags, fill ONLY the axes the user
    # did NOT pass on the command line. CLI payload always wins over the
@@ -8206,5 +8337,6 @@ if __name__ == "__main__":
        override_zone_geometries=overrides_geoms or None,
        override_section_assignments=overrides_section_assignments or None,
        override_image_overrides=overrides_images or None,
+        override_slide_css=_final_override_slide_css,
        reuse_from=args.reuse_from,
    )
--- a/src/slide_css_injector.py
+++ b/src/slide_css_injector.py
@@ -0,0 +1,87 @@
+"""IMP-45 (#74) u3 — slide-level CSS override injector for Phase Z final.html.
+
+Mirror of :func:`src.image_id_stamper.inject_image_overrides_style` contract
+(image_id_stamper.py:226-264) for the new ``slide_css`` override axis
+registered by u1 in :data:`src.user_overrides_io.KNOWN_AXES` and surfaced
+by u2 in :func:`src.mdx_normalizer.normalize_mdx_content` under the
+``slide_overrides.css`` frontmatter key.
+
+Single entry point :
+
+    :func:`inject_slide_css` (html, css) -> str
+
+Semantics (identical contract to image_overrides injector) :
+
+- Empty / falsy ``css`` -> ``html`` returned unchanged (no DOM mutation).
+- Marker-wrapped ``<style>`` block; re-injection replaces inner CSS in
+  place (idempotent on identical input; latest-wins on different input).
+- Injection precedence : (1) before first ``</head>`` (case-insensitive),
+  (2) immediately after the first ``<body ...>`` open tag, (3) at the
+  start of the document. Phase Z ``slide_base.html`` always emits
+  ``</head>`` so path 1 wins for production renders; paths 2/3 are
+  defensive fallbacks for fragment inputs.
+
+Marker sentinels (distinct from image_overrides markers so the two
+injectors can co-exist on the same document without collision; the
+literal form is pinned by the Stage 2 binding contract for IMP-45 /
+issue #74) :
+
+    <!--IMP45-SLIDE-CSS:OPEN-->
+    <!--IMP45-SLIDE-CSS:CLOSE-->
+
+Both injectors target ``</head>`` first, so call order determines DOM
+order. u4 calls ``inject_image_overrides_style`` first (existing Step 13
+behavior) and then ``inject_slide_css``, putting slide-level overrides
+after image overrides in cascade order so the editor-authored slide CSS
+wins ties at the same specificity (intended by IMP-45 scope).
+
+Guardrails :
+
+- No-hardcoding : ``css`` is caller-supplied verbatim. No sample-id or
+  frame-id branches.
+- AI-isolation : pure deterministic Python; no LLM calls.
+- Carve-out (IMP-46 #62) : brand-new module, does not touch the
+  #76 commit ``1186ad8`` cache region.
+"""
+from __future__ import annotations
+
+import re
+
+_IMP45_STYLE_MARKER_OPEN: str = "<!--IMP45-SLIDE-CSS:OPEN-->"
+_IMP45_STYLE_MARKER_CLOSE: str = "<!--IMP45-SLIDE-CSS:CLOSE-->"
+
+_IMP45_STYLE_BLOCK_RE = re.compile(
+    re.escape(_IMP45_STYLE_MARKER_OPEN) + r".*?" + re.escape(_IMP45_STYLE_MARKER_CLOSE),
+    flags=re.DOTALL,
+)
+_HEAD_CLOSE_RE = re.compile(r"</head\s*>", flags=re.IGNORECASE)
+_BODY_OPEN_RE = re.compile(r"<body\b[^>]*>", flags=re.IGNORECASE)
+
+
+def inject_slide_css(html: str, css: str | None) -> str:
+    """Inject a marker-wrapped ``<style>`` block carrying ``css`` into ``html``.
+
+    Empty or ``None`` ``css`` -> ``html`` returned unchanged. Re-injection
+    is idempotent : when a previously-injected marker block is present,
+    its inner CSS is replaced in place.
+
+    Injection precedence : ``</head>`` > ``<body ...>`` > document start.
+    """
+    if not css:
+        return html
+    block = (
+        f"{_IMP45_STYLE_MARKER_OPEN}\n"
+        f"<style>\n{css}\n</style>\n"
+        f"{_IMP45_STYLE_MARKER_CLOSE}"
+    )
+    if _IMP45_STYLE_MARKER_OPEN in html:
+        return _IMP45_STYLE_BLOCK_RE.sub(lambda _m: block, html, count=1)
+    head_close = _HEAD_CLOSE_RE.search(html)
+    if head_close is not None:
+        idx = head_close.start()
+        return html[:idx] + block + "\n" + html[idx:]
+    body_open = _BODY_OPEN_RE.search(html)
+    if body_open is not None:
+        idx = body_open.end()
+        return html[:idx] + "\n" + block + html[idx:]
+    return block + "\n" + html
--- a/src/user_overrides_io.py
+++ b/src/user_overrides_io.py
@@ -5,14 +5,16 @@ auto-restores user choices without re-clicking. Source of truth = MDX-keyed
 file (stem of the MDX path), NOT ``data/runs/<run_id>/`` which mints a fresh
 run_id per ``/api/run`` invocation.

-Schema (5 axes; stable order; IMP-51 #79 u1 added ``image_overrides``):
+Schema (6 axes; stable order; IMP-51 #79 u1 added ``image_overrides``;
+IMP-45 #74 u1 added ``slide_css``):

    {
      "layout":          <string|null>,
      "zone_geometries": {<zone_id>: {"x": float, "y": float, "w": float, "h": float}},
      "zone_sections":   {<zone_id>: [<section_id>, ...]},
      "frames":          {<unit_id>: <template_id>},
-      "image_overrides": {<image_id>: {"x": float, "y": float, "w": float, "h": float}}
+      "image_overrides": {<image_id>: {"x": float, "y": float, "w": float, "h": float}},
+      "slide_css":       <string|null>
    }

 ``image_id`` is the stable identifier emitted by the user-content image
@@ -53,16 +55,17 @@ from typing import Any, Optional
 _PKG_ROOT = Path(__file__).resolve().parent.parent
 DEFAULT_OVERRIDES_ROOT = _PKG_ROOT / "data" / "user_overrides"

-# The five in-scope axes (IMP-51 #79 u1 added ``image_overrides``). Any
-# other top-level key in the file is preserved but ignored by callers —
-# keeps the file forward-compatible with future axes (e.g., zone_sizes)
-# without a schema bump here.
+# The six in-scope axes (IMP-51 #79 u1 added ``image_overrides``; IMP-45
+# #74 u1 added ``slide_css``). Any other top-level key in the file is
+# preserved but ignored by callers — keeps the file forward-compatible
+# with future axes (e.g., zone_sizes) without a schema bump here.
 KNOWN_AXES: tuple[str, ...] = (
    "layout",
    "zone_geometries",
    "zone_sections",
    "frames",
    "image_overrides",
+    "slide_css",
 )

 # Key validation — MDX stem must be safe for filesystem use. Allow
--- a/tests/regression/fixtures/89a_pre_baseline_sha.json
+++ b/tests/regression/fixtures/89a_pre_baseline_sha.json
@@ -40,8 +40,8 @@
    "04.mdx": {
      "mdx_file": "04.mdx",
      "run_id": "89a_baseline_04",
-      "final_html_size_bytes": 27707,
-      "sha256": "2bce45041cdcca6518cd92586c1be9e051a5c98f5a0ad61fdde02604618a1d80",
+      "final_html_size_bytes": 28042,
+      "sha256": "ddb6bf2f8d76ca1f56588a50dd4af5aeb5f45e0a83d5241b83b5932d0c66d41c",
      "pipeline_exit_code": null
    },
    "05.mdx": {
--- a/tests/test_mdx_normalizer.py
+++ b/tests/test_mdx_normalizer.py
@@ -0,0 +1,107 @@
+"""IMP-45 (#74) u2 — frontmatter ``slide_overrides`` surfacing.
+
+Covers ``src.mdx_normalizer.normalize_mdx_content`` and the helper
+``_extract_slide_overrides``. The Stage 2 plan enumerates four cases:
+
+1. Present — nested ``slide_overrides.css`` survives normalization verbatim.
+2. Absent — return dict carries an empty ``slide_overrides`` mapping.
+3. Non-string ``css`` — dropped (fail-closed against typo'd YAML shapes).
+4. Title-only frontmatter — no ``slide_overrides`` key in metadata → ``{}``.
+
+Scope-lock: this unit only adds the new key to the return dict. The four
+pre-existing return keys (``clean_text``/``title``/``images``/``popups``/
+``tables``/``sections``) are asserted unchanged at the structural level.
+"""
+from __future__ import annotations
+
+from src.mdx_normalizer import _extract_slide_overrides, normalize_mdx_content
+
+
+_CSS_BLOCK = "<style>.f29b__col_right { width: 320px; }</style>"
+
+
+def _mdx_with_frontmatter(fm_body: str, body: str = "# 제목\n\n본문 한 줄.\n") -> str:
+    return f"---\n{fm_body}---\n{body}"
+
+
+# -- case 1: present (nested css string survives verbatim) ------------------
+
+
+def test_normalize_surfaces_nested_slide_overrides_css():
+    raw = _mdx_with_frontmatter(
+        "title: 04 sample\n"
+        "slide_overrides:\n"
+        f"  css: \"{_CSS_BLOCK}\"\n"
+    )
+
+    result = normalize_mdx_content(raw)
+
+    assert result["slide_overrides"] == {"css": _CSS_BLOCK}
+    # Other axes unaffected by the new key.
+    assert result["title"] == "04 sample"
+    assert "본문" in result["clean_text"]
+
+
+# -- case 2: absent (no slide_overrides key in frontmatter) -----------------
+
+
+def test_normalize_returns_empty_slide_overrides_when_key_absent():
+    raw = _mdx_with_frontmatter("title: 03 sample\n")
+
+    result = normalize_mdx_content(raw)
+
+    assert result["slide_overrides"] == {}
+    # Confirm key is always present (callers can rely on .get without default).
+    assert "slide_overrides" in result
+
+
+# -- case 3: non-string css (fail-closed drop) ------------------------------
+
+
+def test_normalize_drops_non_string_css_under_slide_overrides():
+    # YAML list under .css should be dropped; sibling unknown keys survive
+    # so the future generalization path (e.g., slide_overrides.js) stays
+    # forward-compatible per the Stage 2 plan.
+    raw = _mdx_with_frontmatter(
+        "title: typo case\n"
+        "slide_overrides:\n"
+        "  css:\n"
+        "    - .f29b__col_right { width: 320px; }\n"
+        "  note: experimental sibling\n"
+    )
+
+    result = normalize_mdx_content(raw)
+
+    assert "css" not in result["slide_overrides"]
+    assert result["slide_overrides"].get("note") == "experimental sibling"
+
+
+# -- case 4: title-only frontmatter (no slide_overrides at all) -------------
+
+
+def test_normalize_title_only_frontmatter_yields_empty_slide_overrides():
+    raw = _mdx_with_frontmatter("title: title only\n")
+
+    result = normalize_mdx_content(raw)
+
+    assert result["title"] == "title only"
+    assert result["slide_overrides"] == {}
+
+
+# -- direct helper coverage (defensive against future return-shape drift) ---
+
+
+def test_extract_slide_overrides_non_mapping_returns_empty_dict():
+    # Frontmatter parsers can yield odd types if the user writes
+    # ``slide_overrides: 42`` or ``slide_overrides: ".x{}"``. The helper
+    # must coerce to ``{}`` rather than raise.
+    for bad in (None, 42, "literal string", ["css"]):
+        assert _extract_slide_overrides({"slide_overrides": bad}) == {}
+
+
+def test_extract_slide_overrides_passes_through_unknown_siblings():
+    payload = {"slide_overrides": {"css": ".a{}", "js": "console.log(1)"}}
+    assert _extract_slide_overrides(payload) == {
+        "css": ".a{}",
+        "js": "console.log(1)",
+    }
--- a/tests/test_phase_z2_cli_overrides.py
+++ b/tests/test_phase_z2_cli_overrides.py
@@ -56,6 +56,8 @@ def _exec_main_block(
        override_zone_geometries=None,
        override_section_assignments=None,
        override_image_overrides=None,
+        override_slide_css=None,
+        reuse_from=None,
    ):
        captured["mdx_path"] = mdx_path
        captured["run_id"] = run_id
@@ -64,6 +66,8 @@ def _exec_main_block(
        captured["override_zone_geometries"] = override_zone_geometries
        captured["override_section_assignments"] = override_section_assignments
        captured["override_image_overrides"] = override_image_overrides
+        captured["override_slide_css"] = override_slide_css
+        captured["reuse_from"] = reuse_from

    monkeypatch.setattr(_pz2, "run_phase_z2_mvp1", _fake_run)
    monkeypatch.setattr(sys, "argv", argv)
@@ -346,3 +350,136 @@ def test_image_override_does_not_leak_into_sibling_axes(tmp_path, monkeypatch):
    assert captured["override_frames"] is None
    assert captured["override_zone_geometries"] is None
    assert captured["override_section_assignments"] is None
+
+
+# -- IMP-45 (#74) u5 — slide-level CSS override CLI surface ----------------
+#
+# Six focused cases mirror the --override-image pattern above:
+#   1. neither flag      → kwarg None (fall-back to MDX frontmatter at u4)
+#   2. --override-slide-css inline TEXT → kwarg passes verbatim
+#   3. --slide-css-file PATH UTF-8 read → kwarg = file contents
+#   4. both flags set    → sys.exit(2) with mutual-exclusion stderr
+#   5. --slide-css-file missing path    → sys.exit(2) with not-found stderr
+#   6. --slide-css-file non-UTF-8 bytes → sys.exit(2) with utf-8 stderr
+
+
+def test_no_slide_css_override_forwards_none(tmp_path, monkeypatch):
+    """Neither --override-slide-css nor --slide-css-file → kwarg = None."""
+    _redirect_overrides_root(tmp_path, monkeypatch)
+    captured: dict[str, Any] = {}
+    _exec_main_block(
+        captured, ["src.phase_z2_pipeline", "03.mdx"], monkeypatch,
+    )
+
+    assert captured["override_slide_css"] is None
+
+
+def test_inline_slide_css_override_forwards_verbatim(tmp_path, monkeypatch):
+    """--override-slide-css TEXT → kwarg = TEXT (verbatim, no `<style>` wrap)."""
+    _redirect_overrides_root(tmp_path, monkeypatch)
+    captured: dict[str, Any] = {}
+    _exec_main_block(
+        captured,
+        [
+            "src.phase_z2_pipeline",
+            "03.mdx",
+            "--override-slide-css",
+            ".slide { background: red; }",
+        ],
+        monkeypatch,
+    )
+
+    assert captured["override_slide_css"] == ".slide { background: red; }"
+
+
+def test_slide_css_file_override_reads_utf8(tmp_path, monkeypatch):
+    """--slide-css-file PATH → kwarg = UTF-8 decoded file contents."""
+    _redirect_overrides_root(tmp_path, monkeypatch)
+    css_payload = ".slide-body { color: #1e293b; } /* 한글 주석 */\n"
+    css_path = tmp_path / "slide_override.css"
+    css_path.write_text(css_payload, encoding="utf-8")
+    captured: dict[str, Any] = {}
+    _exec_main_block(
+        captured,
+        [
+            "src.phase_z2_pipeline",
+            "03.mdx",
+            "--slide-css-file",
+            str(css_path),
+        ],
+        monkeypatch,
+    )
+
+    assert captured["override_slide_css"] == css_payload
+
+
+def test_slide_css_both_flags_set_exits(tmp_path, monkeypatch, capsys):
+    """--override-slide-css + --slide-css-file → sys.exit(2)."""
+    _redirect_overrides_root(tmp_path, monkeypatch)
+    css_path = tmp_path / "slide_override.css"
+    css_path.write_text(".slide { color: red; }\n", encoding="utf-8")
+    captured: dict[str, Any] = {}
+    with pytest.raises(SystemExit) as excinfo:
+        _exec_main_block(
+            captured,
+            [
+                "src.phase_z2_pipeline",
+                "03.mdx",
+                "--override-slide-css",
+                ".slide { color: blue; }",
+                "--slide-css-file",
+                str(css_path),
+            ],
+            monkeypatch,
+        )
+
+    assert excinfo.value.code == 2
+    err = capsys.readouterr().err
+    assert "--override-slide-css and --slide-css-file are mutually exclusive" in err
+
+
+def test_slide_css_file_missing_path_exits(tmp_path, monkeypatch, capsys):
+    """--slide-css-file with non-existent PATH → sys.exit(2)."""
+    _redirect_overrides_root(tmp_path, monkeypatch)
+    missing_path = tmp_path / "does_not_exist.css"
+    captured: dict[str, Any] = {}
+    with pytest.raises(SystemExit) as excinfo:
+        _exec_main_block(
+            captured,
+            [
+                "src.phase_z2_pipeline",
+                "03.mdx",
+                "--slide-css-file",
+                str(missing_path),
+            ],
+            monkeypatch,
+        )
+
+    assert excinfo.value.code == 2
+    err = capsys.readouterr().err
+    assert "--slide-css-file path does not exist" in err
+    assert str(missing_path) in err
+
+
+def test_slide_css_file_non_utf8_exits(tmp_path, monkeypatch, capsys):
+    """--slide-css-file with non-UTF-8 bytes → sys.exit(2)."""
+    _redirect_overrides_root(tmp_path, monkeypatch)
+    bad_path = tmp_path / "latin1.css"
+    # 0xff is a stand-alone invalid UTF-8 start byte; strict decode raises.
+    bad_path.write_bytes(b".slide { color: \xff; }\n")
+    captured: dict[str, Any] = {}
+    with pytest.raises(SystemExit) as excinfo:
+        _exec_main_block(
+            captured,
+            [
+                "src.phase_z2_pipeline",
+                "03.mdx",
+                "--slide-css-file",
+                str(bad_path),
+            ],
+            monkeypatch,
+        )
+
+    assert excinfo.value.code == 2
+    err = capsys.readouterr().err
+    assert "--slide-css-file must be UTF-8 encoded" in err
--- a/tests/test_phase_z2_cli_reuse_from.py
+++ b/tests/test_phase_z2_cli_reuse_from.py
@@ -62,6 +62,7 @@ def _exec_main_block(
        override_zone_geometries=None,
        override_section_assignments=None,
        override_image_overrides=None,
+        override_slide_css=None,
        reuse_from=None,
    ):
        captured["called"] = True
@@ -72,6 +73,7 @@ def _exec_main_block(
        captured["override_zone_geometries"] = override_zone_geometries
        captured["override_section_assignments"] = override_section_assignments
        captured["override_image_overrides"] = override_image_overrides
+        captured["override_slide_css"] = override_slide_css
        captured["reuse_from"] = reuse_from

    monkeypatch.setattr(_pz2, "run_phase_z2_mvp1", _fake_run)
--- a/tests/test_phase_z2_slide_css_smoke.py
+++ b/tests/test_phase_z2_slide_css_smoke.py
@@ -0,0 +1,101 @@
+"""IMP-45 (#74) u6 — subprocess smoke for the slide-level CSS override axis.
+
+End-to-end guard that the ``slide_overrides.css`` frontmatter axis added
+in u2 propagates through the pipeline (u4) and lands in ``final.html``
+via :func:`src.slide_css_injector.inject_slide_css` (u3).
+
+The fixture is the new ``slide_overrides.css`` frontmatter block in
+``samples/mdx_batch/04.mdx`` (u6 migration of the legacy frontend-only
+``MDX04_DEFAULT_OVERRIDE_CSS`` constant). The pipeline is spawned via
+``python -m src.phase_z2_pipeline 04.mdx <run_id>`` so the assertion
+applies to the on-disk artifact CI / CLI / regression all observe, not
+to a live iframe view.
+
+The subprocess returncode is intentionally NOT asserted: mdx04 has known
+downstream issues (see ``test_pipeline_smoke_imp85.py`` —
+``test_mdx04_no_longer_emits_imp85_crash_signature``) that are tracked
+on a separate axis. Step 13 runs before the downstream failure surface,
+so ``final.html`` is written with the injected slide CSS marker
+regardless. The test asserts ``final.html`` exists and contains both
+the IMP-45 sentinel marker and a distinctive CSS substring from the
+migrated frontmatter block.
+"""
+from __future__ import annotations
+
+import subprocess
+import sys
+import uuid
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+SAMPLES_DIR = REPO_ROOT / "samples" / "mdx_batch"
+RUNS_DIR = REPO_ROOT / "data" / "runs"
+
+# IMP-45 (#74) u3 marker sentinel emitted by
+# :func:`src.slide_css_injector.inject_slide_css` around the injected
+# ``<style>`` block. Match the ``_IMP45_STYLE_MARKER_OPEN`` constant in
+# ``src/slide_css_injector.py`` byte-for-byte.
+IMP45_OPEN_MARKER = "<!--IMP45-SLIDE-CSS:OPEN-->"
+IMP45_CLOSE_MARKER = "<!--IMP45-SLIDE-CSS:CLOSE-->"
+
+# Distinctive substring from the migrated frontmatter block in
+# ``samples/mdx_batch/04.mdx``. ``f29b__cell:nth-child(n+3)`` is unique
+# to the MDX04 slide-level override CSS and does not appear elsewhere in
+# the slide_base / partial templates, so its presence in ``final.html``
+# is sufficient evidence that the frontmatter axis fed the injector.
+MDX04_DISTINCTIVE_CSS_SUBSTRING = ".f29b__cell:nth-child(n+3)"
+
+
+def _run_pipeline(mdx_name: str, run_id: str, timeout: int = 240) -> subprocess.CompletedProcess:
+    """Spawn ``python -m src.phase_z2_pipeline <mdx> <run_id>``."""
+    return subprocess.run(
+        [
+            sys.executable,
+            "-m",
+            "src.phase_z2_pipeline",
+            str(SAMPLES_DIR / mdx_name),
+            run_id,
+        ],
+        capture_output=True,
+        text=True,
+        timeout=timeout,
+        cwd=str(REPO_ROOT),
+    )
+
+
+def _unique_run_id(prefix: str) -> str:
+    return f"{prefix}_imp45_slide_css_smoke_{uuid.uuid4().hex[:8]}"
+
+
+def test_mdx04_slide_overrides_css_lands_in_final_html() -> None:
+    """mdx04 ``slide_overrides.css`` frontmatter must reach ``final.html``.
+
+    Contract pins both the IMP-45 marker sentinel and a distinctive CSS
+    substring from the migrated frontmatter block so a regression in
+    either the frontmatter extractor (u2), the kwarg forwarding (u4),
+    or the injector (u3) is caught by this single smoke.
+    """
+    run_id = _unique_run_id("mdx04")
+    cp = _run_pipeline("04.mdx", run_id)
+
+    final_html_path = RUNS_DIR / run_id / "phase_z2" / "final.html"
+    assert final_html_path.is_file(), (
+        f"final.html not found at {final_html_path}\n"
+        f"--- stderr tail ---\n{cp.stderr[-1500:]}\n"
+        f"--- stdout tail ---\n{cp.stdout[-1500:]}"
+    )
+    html = final_html_path.read_text(encoding="utf-8")
+
+    assert IMP45_OPEN_MARKER in html, (
+        f"IMP-45 open marker missing from mdx04 final.html ({final_html_path}).\n"
+        f"slide_overrides.css frontmatter axis did not reach the injector."
+    )
+    assert IMP45_CLOSE_MARKER in html, (
+        f"IMP-45 close marker missing from mdx04 final.html ({final_html_path}).\n"
+        f"Marker wrap appears unbalanced — check inject_slide_css() output."
+    )
+    assert MDX04_DISTINCTIVE_CSS_SUBSTRING in html, (
+        f"Migrated frontmatter CSS substring "
+        f"{MDX04_DISTINCTIVE_CSS_SUBSTRING!r} missing from mdx04 final.html "
+        f"({final_html_path}). The slide_overrides.css block did not propagate."
+    )
--- a/tests/test_slide_css_injector.py
+++ b/tests/test_slide_css_injector.py
@@ -0,0 +1,100 @@
+"""IMP-45 (#74) u3 — tests for :mod:`src.slide_css_injector`.
+
+Mirrors the inject_image_overrides_style test pattern in
+``tests/test_image_id_stamper.py`` (lines 306-377) for the new
+``slide_css`` axis. Eight cases :
+
+1. empty css returns html unchanged
+2. None css returns html unchanged (mirror of empty-css guard for the
+   typed ``str | None`` signature)
+3. inserts before </head> (precedence path 1)
+4. case-insensitive head close (precedence path 1, uppercase variant)
+5. body-open fallback when no </head> (precedence path 2)
+6. document-start fallback when neither head nor body present (path 3)
+7. idempotent on second call with identical css
+8. replaces existing block when re-called with different css (latest-wins)
+
+Plus one additional guard :
+
+9. marker comments wrap the injected <style> block (open precedes close,
+   <style> sits between them)
+"""
+from __future__ import annotations
+
+from src.slide_css_injector import inject_slide_css
+
+
+_OPEN_MARKER = "<!--IMP45-SLIDE-CSS:OPEN-->"
+_CLOSE_MARKER = "<!--IMP45-SLIDE-CSS:CLOSE-->"
+
+
+def test_inject_slide_css_empty_string_returns_html_unchanged():
+    html = "<html><head></head><body>x</body></html>"
+    assert inject_slide_css(html, "") == html
+
+
+def test_inject_slide_css_none_returns_html_unchanged():
+    html = "<html><head></head><body>x</body></html>"
+    assert inject_slide_css(html, None) == html
+
+
+def test_inject_slide_css_inserts_before_head_close():
+    html = "<html><head><title>t</title></head><body>x</body></html>"
+    out = inject_slide_css(html, ".x { color: red; }")
+    assert "<style>" in out
+    head_idx = out.lower().index("</head>")
+    body_idx = out.lower().index("<body")
+    style_idx = out.index("<style>")
+    assert style_idx < head_idx < body_idx
+
+
+def test_inject_slide_css_case_insensitive_head_close():
+    html = "<HTML><HEAD></HEAD><BODY>x</BODY></HTML>"
+    out = inject_slide_css(html, ".x { color: red; }")
+    assert "<style>" in out
+    assert out.index("<style>") < out.upper().index("</HEAD>")
+
+
+def test_inject_slide_css_falls_back_to_body_open_when_no_head():
+    html = "<body>x</body>"
+    out = inject_slide_css(html, ".x { color: red; }")
+    assert "<style>" in out
+    body_open_end = out.index(">", out.index("<body")) + 1
+    assert out[body_open_end:].lstrip().startswith(_OPEN_MARKER)
+
+
+def test_inject_slide_css_falls_back_to_document_start_when_no_head_or_body():
+    html = "<div>fragment</div>"
+    out = inject_slide_css(html, ".x { color: red; }")
+    assert out.startswith(_OPEN_MARKER)
+    assert "<style>" in out
+    assert out.rstrip().endswith("</div>")
+
+
+def test_inject_slide_css_is_idempotent_on_second_call():
+    html = "<html><head></head><body>x</body></html>"
+    css = ".x { color: red; }"
+    once = inject_slide_css(html, css)
+    twice = inject_slide_css(once, css)
+    assert twice == once
+    assert once.count(_OPEN_MARKER) == 1
+    assert twice.count(_OPEN_MARKER) == 1
+
+
+def test_inject_slide_css_replaces_existing_block_with_new_css():
+    html = "<html><head></head><body>x</body></html>"
+    first = inject_slide_css(html, ".old { color: red; }")
+    second = inject_slide_css(first, ".new { color: blue; }")
+    assert ".old" not in second
+    assert ".new" in second
+    assert second.count(_OPEN_MARKER) == 1
+
+
+def test_inject_slide_css_wraps_block_with_marker_comments():
+    html = "<html><head></head><body>x</body></html>"
+    out = inject_slide_css(html, ".x { color: red; }")
+    assert _OPEN_MARKER in out
+    assert _CLOSE_MARKER in out
+    s = out.index(_OPEN_MARKER)
+    e = out.index(_CLOSE_MARKER)
+    assert s < out.index("<style>") < out.index("</style>") < e
--- a/tests/test_user_overrides_io.py
+++ b/tests/test_user_overrides_io.py
@@ -1,9 +1,10 @@
 """IMP-52 (#80) u8 — backend tests for ``src.user_overrides_io``.

 Covers the persisted axes called out in the Stage 2 plan
-(IMP-51 #79 u1 extended this to 5 axes by adding ``image_overrides``):
+(IMP-51 #79 u1 extended this to 5 axes by adding ``image_overrides``;
+IMP-45 #74 u1 extended to 6 axes by adding ``slide_css``):

-1. Round-trip ``save`` → ``load`` (5 KNOWN_AXES + foreign top-level keys).
+1. Round-trip ``save`` → ``load`` (6 KNOWN_AXES + foreign top-level keys).
 2. Unknown-key passthrough (foreign axes preserved across partial merges).
 3. Missing / corrupt / non-object behavior (graceful ``{}`` + stderr warning).
 4. Invalid keys (``InvalidOverrideKey`` raised on traversal / separators /
@@ -119,13 +120,20 @@ def _full_payload() -> dict:
        "image_overrides": {
            "img-1": {"x": 10.0, "y": 20.0, "w": 30.0, "h": 25.0},
        },
+        "slide_css": "<style>.slide .frame-process-product .label { font-size: 14px; }</style>",
    }


 def test_known_axes_includes_image_overrides():
-    """IMP-51 #79 u1 — ``image_overrides`` is a known axis (5 total)."""
+    """IMP-51 #79 u1 — ``image_overrides`` is a known axis (now 6 total)."""
    assert "image_overrides" in KNOWN_AXES
-    assert len(KNOWN_AXES) == 5
+    assert len(KNOWN_AXES) == 6
+
+
+def test_known_axes_includes_slide_css():
+    """IMP-45 #74 u1 — ``slide_css`` is a known axis (6 total)."""
+    assert "slide_css" in KNOWN_AXES
+    assert len(KNOWN_AXES) == 6


 def test_save_then_load_round_trip(tmp_path):
@@ -152,6 +160,7 @@ def test_save_partial_payload_preserves_other_axes(tmp_path):
    assert loaded["zone_sections"] == _full_payload()["zone_sections"]
    assert loaded["frames"] == _full_payload()["frames"]
    assert loaded["image_overrides"] == _full_payload()["image_overrides"]
+    assert loaded["slide_css"] == _full_payload()["slide_css"]


 def test_save_partial_image_overrides_preserves_other_axes(tmp_path):
@@ -173,6 +182,7 @@ def test_save_partial_image_overrides_preserves_other_axes(tmp_path):
    assert loaded["zone_geometries"] == _full_payload()["zone_geometries"]
    assert loaded["zone_sections"] == _full_payload()["zone_sections"]
    assert loaded["frames"] == _full_payload()["frames"]
+    assert loaded["slide_css"] == _full_payload()["slide_css"]


 def test_save_axis_replaces_not_deep_merges(tmp_path):
@@ -231,9 +241,17 @@ def test_save_writes_pretty_sorted_json_for_diffability(tmp_path):
    pos_frames = raw.index('"frames"')
    pos_image_overrides = raw.index('"image_overrides"')
    pos_layout = raw.index('"layout"')
+    pos_slide_css = raw.index('"slide_css"')
    pos_zg = raw.index('"zone_geometries"')
    pos_zs = raw.index('"zone_sections"')
-    assert pos_frames < pos_image_overrides < pos_layout < pos_zg < pos_zs
+    assert (
+        pos_frames
+        < pos_image_overrides
+        < pos_layout
+        < pos_slide_css
+        < pos_zg
+        < pos_zs
+    )


 def test_save_leaves_no_tmp_file_on_success(tmp_path):