Opaque panel header and toolbar; explain empty results

The theme's table header colour is a translucent tint, so rows scrolling
underneath made the column bar unreadable. Paint it over the solid
editor background. An empty search now asks the .NET Solution Launcher
which projects the language server loaded and says so, with a reload
button, instead of a bare "No references found".

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0169iPWwKHZoBTNN9qwXiwqk

media/panel.css

@@ -40,6 +40,8 @@ body {
     padding: 4px 8px;
     border-bottom: 1px solid var(--vscode-panel-border, transparent);
     flex: 0 0 auto;
+    /* Solid: rows scroll underneath, and a see-through bar over code is unreadable. */
+    background: var(--vscode-editor-background);
 }
 
 #summary {
@@ -112,7 +114,12 @@ body {
     display: grid;
     grid-template-columns: var(--grid);
     height: var(--header-height);
-    background: var(--vscode-keybindingTable-headerBackground, var(--vscode-editor-background));
+    /* The theme's header colour is usually a translucent tint, so it is painted over the
+       solid editor background; otherwise rows scrolling underneath show through it. */
+    background-color: var(--vscode-editor-background);
+    background-image: linear-gradient(
+        var(--vscode-keybindingTable-headerBackground, transparent),
+        var(--vscode-keybindingTable-headerBackground, transparent));
     border-bottom: 1px solid var(--vscode-panel-border, var(--vscode-editorWidget-border));
     user-select: none;
 }