Fix sticky header and opaque dark mode header backgrounds

- Add max-height to table container so sticky header works on scroll
- Replace transparent dark mode header gradient with opaque colors

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

Author: 3 people

docs/projects/grcengineering-cheat-sheet/index.html

@@ -167,6 +167,7 @@
     0 1px 4px var(--shadow);
   border: 1px solid var(--border);
   background: var(--bg-card);
+  max-height: calc(100vh - 100px);
 }
 
 /* ── TABLE ── */
@@ -193,7 +194,7 @@
   white-space: nowrap;
 }
 [data-theme="dark"] thead th {
-  background: linear-gradient(135deg, rgba(255,168,79,0.15), rgba(27,149,193,0.1));
+  background: linear-gradient(135deg, #2a1f3e, #1a2a3e);
   border-bottom-color: var(--border-header);
 }
 thead th:first-child {