[theme] css rule tag function

src/vs/platform/theme/common/themeService.ts

@@ -106,4 +106,22 @@ platform.Registry.add(Extensions.ThemingContribution, themingRegistry);
 
 export function registerThemingParticipant(participant: IThemingParticipant): IDisposable {
 	return themingRegistry.onThemeChange(participant);
+}
+
+/**
+ * Tag function for strings containing css rules
+ */
+export function cssRule(literals, ...placeholders) {
+	let result = '';
+	for (let i = 0; i < placeholders.length; i++) {
+		result += literals[i];
+		let placeholder = placeholders[i];
+		if (placeholder === null) {
+			result += 'transparent';
+		} else {
+			result += placeholder.toString();
+		}
+	}
+	result += literals[literals.length - 1];
+	return result;
 }
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