Fix command palette CSS

Theia changed their CSS variables in
eclipse-theia/theia#6722.
This change adapts the variable names for the command palette.

css/command-palette.css

@@ -15,20 +15,30 @@
  ********************************************************************************/
 
 .command-palette {
-    box-shadow: var(--theia-border-width) var(--theia-border-width) var(--theia-border-color0);
-    background-color: var(--theia-layout-color0);
+    box-shadow: var(--theia-border-width) var(--theia-border-width) var(--theia-widget-shadow);
+    background-color: var(--theia-titleBar-activeBackground);
+}
+
+.command-palette input {
+    border-color: var(--theia-panelInput-border);
+    background: var(--theia-input-background);
+    color: var(--theia-input-foreground);
+}
+
+.command-palette input:hover {
+    color: var(--theia-button-hoverBackground);
 }
 
 .command-palette-suggestions {
-    background-color: inherit;
+    background-color: var(--theia-titleBar-activeBackground);
 }
 
 .command-palette-suggestions>div:hover:not(.group) {
-    background: var(--theia-layout-color2);
+    background: var(--theia-editorHoverWidget-background);
 }
 
 .command-palette-suggestions>div.selected {
-    background: var(--theia-accent-color4);
+    background: var(--theia-menubar-selectionBackground);
 }
 
 .command-palette .loading {