Use theme colors for webview scrollbars

Fixes #59320

Switches webview scrollbars to use themecolors instead of hardcoded values

src/vs/workbench/parts/webview/electron-browser/webview-pre.js

@@ -269,33 +269,13 @@
 			}
 
 			::-webkit-scrollbar-thumb {
-				background-color: rgba(121, 121, 121, 0.4);
+				background-color: var(--vscode-scrollbarSlider-background);
 			}
-			body.vscode-light::-webkit-scrollbar-thumb {
-				background-color: rgba(100, 100, 100, 0.4);
-			}
-			body.vscode-high-contrast::-webkit-scrollbar-thumb {
-				background-color: rgba(111, 195, 223, 0.3);
-			}
-
 			::-webkit-scrollbar-thumb:hover {
-				background-color: rgba(100, 100, 100, 0.7);
-			}
-			body.vscode-light::-webkit-scrollbar-thumb:hover {
-				background-color: rgba(100, 100, 100, 0.7);
+				background-color: var(--vscode-scrollbarSlider-hoverBackground);
 			}
-			body.vscode-high-contrast::-webkit-scrollbar-thumb:hover {
-				background-color: rgba(111, 195, 223, 0.8);
-			}
-
 			::-webkit-scrollbar-thumb:active {
-				background-color: rgba(85, 85, 85, 0.8);
-			}
-			body.vscode-light::-webkit-scrollbar-thumb:active {
-				background-color: rgba(0, 0, 0, 0.6);
-			}
-			body.vscode-high-contrast::-webkit-scrollbar-thumb:active {
-				background-color: rgba(111, 195, 223, 0.8);
+				background-color: var(--vscode-scrollbarSlider-activeBackground);
 			}
 			`;
 			if (newDocument.head.hasChildNodes()) {