feat(theme): add brown and orange background gradients

themes/default.json

@@ -18,6 +18,16 @@
     "color.bg.brand.stop.42": "#123328",
     "color.bg.brand.stop.78": "#266651",
     "color.bg.brand.stop.100": "#205241",
+    "color.bg.brown.stop.0": "#352d1d",
+    "color.bg.brown.stop.12": "#2f281c",
+    "color.bg.brown.stop.42": "#3e3523",
+    "color.bg.brown.stop.78": "#897445",
+    "color.bg.brown.stop.100": "#604f32",
+    "color.bg.orange.stop.0": "#bc4c00",
+    "color.bg.orange.stop.12": "#883700",
+    "color.bg.orange.stop.42": "#cc5200",
+    "color.bg.orange.stop.78": "#f87725",
+    "color.bg.orange.stop.100": "#eb5f00",
     "surface.action.primary.stop.0": "#1f8265",
     "surface.action.primary.stop.30": "#165c47",
     "surface.action.primary.stop.65": "#114838",