testing: fix glitch with test view widget and sticky scroll (microsof…

…t#200418)

Fixes microsoft#200192

src/vs/workbench/contrib/testing/browser/testingOutputPeek.ts

@@ -71,6 +71,7 @@ import { ITelemetryService } from 'vs/platform/telemetry/common/telemetry';
 import { TerminalCapability } from 'vs/platform/terminal/common/capabilities/capabilities';
 import { TerminalCapabilityStore } from 'vs/platform/terminal/common/capabilities/terminalCapabilityStore';
 import { formatMessageForTerminal } from 'vs/platform/terminal/common/terminalStrings';
+import { editorBackground } from 'vs/platform/theme/common/colorRegistry';
 import { widgetClose } from 'vs/platform/theme/common/iconRegistry';
 import { IColorTheme, IThemeService } from 'vs/platform/theme/common/themeService';
 import { IWorkspaceContextService } from 'vs/platform/workspace/common/workspace';
@@ -959,10 +960,11 @@ class TestResultsPeek extends PeekViewWidget {
 	private applyTheme(theme: IColorTheme) {
 		const borderColor = theme.getColor(testingPeekBorder) || Color.transparent;
 		const headerBg = theme.getColor(testingPeekHeaderBackground) || Color.transparent;
+		const editorBg = theme.getColor(editorBackground);
 		this.style({
 			arrowColor: borderColor,
 			frameColor: borderColor,
-			headerBackgroundColor: headerBg,
+			headerBackgroundColor: editorBg && headerBg ? headerBg.makeOpaque(editorBg) : headerBg,
 			primaryHeadingColor: theme.getColor(peekViewTitleForeground),
 			secondaryHeadingColor: theme.getColor(peekViewTitleInfoForeground)
 		});