Move server styles into its own scss file; add a little polish

src/core/components/layouts/base.jsx

@@ -94,7 +94,7 @@ export default class BaseLayout extends React.Component {
             ) : null }
 
             { servers && servers.size ? (
-              <div className="server-container">
+              <div className="global-server-container">
                 <span className="servers-title">Server</span>
                 <Col className="servers wrapper" mobile={12}>
                   <Servers

src/core/plugins/oas3/components/operation-servers.jsx

@@ -74,14 +74,16 @@ export default class OperationServers extends React.Component {
     const serversToDisplay = operationServers || pathServers
     const displaying = operationServers ? "operation" : "path"
 
-    return <div className="opblock-section">
+    return <div className="opblock-section operation-servers">
       <div className="opblock-section-header">
         <div className="tab-header">
           <h4 className="opblock-title">Servers</h4>
         </div>
       </div>
       <div className="opblock-description-wrapper">
-        <h4>These {displaying}-level options override the global server options.</h4>
+        <h4 className="message">
+          These {displaying}-level options override the global server options.
+        </h4>
         <Servers
           servers={serversToDisplay}
           currentServer={this.getSelectedServer()}

src/core/plugins/oas3/components/servers.jsx

@@ -93,7 +93,7 @@ export default class Servers extends React.Component {
     let shouldShowVariableUI = currentServerVariableDefs.size !== 0
 
     return (
-      <div>
+      <div className="servers">
         <label htmlFor="servers">
           <select onChange={ this.onServerChange }>
             { servers.valueSeq().map(