Tweak overlay contrast (fixes #19419, fixes #19051)

src/vs/workbench/parts/welcome/overlay/browser/welcomeOverlay.css

@@ -23,12 +23,16 @@
 	transition: filter .25s, opacity .2s;
 }
 
-#workbench\.parts\.editor.blur-background {
-	filter: blur(3px);
-	opacity: .28;
+.monaco-workbench.blur-background #workbench\.parts\.panel,
+.monaco-workbench.blur-background #workbench\.parts\.sidebar,
+.monaco-workbench.blur-background #workbench\.parts\.editor {
+	filter: blur(2px);
+	opacity: .4;
 }
 
-.hc-black #workbench\.parts\.editor.blur-background {
+.hc-black .monaco-workbench.blur-background #workbench\.parts\.panel,
+.hc-black .monaco-workbench.blur-background #workbench\.parts\.sidebar,
+.hc-black .monaco-workbench.blur-background #workbench\.parts\.editor {
 	opacity: .2;
 }
 

src/vs/workbench/parts/welcome/overlay/browser/welcomeOverlay.ts

@@ -193,9 +193,9 @@ class WelcomeOverlay {
 
 	public show() {
 		if (this._overlay.style('display') !== 'block') {
-			const welcomePage = document.getElementById('workbench.parts.editor') as HTMLDivElement;
 			this._overlay.display('block');
-			dom.addClass(welcomePage, 'blur-background');
+			const workbench = document.querySelector('.monaco-workbench') as HTMLElement;
+			dom.addClass(workbench, 'blur-background');
 			this._overlayVisible.set(true);
 		}
 	}
@@ -203,8 +203,8 @@ class WelcomeOverlay {
 	public hide() {
 		if (this._overlay.style('display') !== 'none') {
 			this._overlay.display('none');
-			const welcomePage = document.getElementById('workbench.parts.editor') as HTMLDivElement;
-			dom.removeClass(welcomePage, 'blur-background');
+			const workbench = document.querySelector('.monaco-workbench') as HTMLElement;
+			dom.removeClass(workbench, 'blur-background');
 			this._overlayVisible.reset();
 		}
 	}