Fix prerelease banner contrast and baseline website-accessibility code blocks

Author: cwickham

_axe-baseline.json

@@ -9,7 +9,19 @@
     },
     {
       "signature": "scrollable-region-focusable :: .code-with-filename > .code-with-filename-file > pre",
-      "pages": ["docs/extensions/brand.html", "docs/extensions/filters.html", "docs/extensions/formats.html", "docs/extensions/revealjs.html", "docs/extensions/shortcodes.html", "docs/journals/formats.html", "docs/websites/website-drafts.html"],
+      "pages": ["docs/extensions/brand.html", "docs/extensions/filters.html", "docs/extensions/formats.html", "docs/extensions/revealjs.html", "docs/extensions/shortcodes.html", "docs/journals/formats.html", "docs/websites/website-accessibility.html", "docs/websites/website-drafts.html"],
+      "impact": "serious",
+      "note": "upstream: quarto-dev/quarto-cli#14378. Scrollable code blocks and cell outputs have no tabindex, so keyboard users cannot scroll them. Clears when quarto-dev/quarto-cli#14816 ships."
+    },
+    {
+      "signature": "scrollable-region-focusable :: #your-first-scan > pre",
+      "pages": ["docs/websites/website-accessibility.html"],
+      "impact": "serious",
+      "note": "upstream: quarto-dev/quarto-cli#14378. Scrollable code blocks and cell outputs have no tabindex, so keyboard users cannot scroll them. Clears when quarto-dev/quarto-cli#14816 ships."
+    },
+    {
+      "signature": "scrollable-region-focusable :: #checking-accessibility-in-ci > .code-with-filename > .code-with-filename-file > pre",
+      "pages": ["docs/websites/website-accessibility.html"],
       "impact": "serious",
       "note": "upstream: quarto-dev/quarto-cli#14378. Scrollable code blocks and cell outputs have no tabindex, so keyboard users cannot scroll them. Clears when quarto-dev/quarto-cli#14816 ships."
     },

_quarto-prerelease-docs.yml

@@ -19,3 +19,4 @@ format:
     toc: true
     theme:
       light: [cosmo, theme.scss, theme-prerelease-docs.scss]
+      dark: [cosmo, theme-dark.scss, theme-prerelease-docs.scss]

theme-prerelease-docs.scss

@@ -1,8 +1,10 @@
 /*-- scss:rules --*/
 
+// #e60033 keeps the red but gives white text 4.76:1 (WCAG 1.4.3 needs 4.5:1).
+// Cosmo's $danger (#ff0039) gives only 3.95:1.
 #quarto-announcement {
   font-size: 1em;
   font-weight: bold;
   color: $white;
-  background-color: $danger; 
-}
+  background-color: #e60033;
+}