src/vs/css.build.ts/rewriteUrls
export function rewriteUrls(originalFile: string, newFile: string, contents: string): string {
	return CSSPluginUtilities.replaceURL(contents, (url) => {
		const absoluteUrl = CSSPluginUtilities.joinPaths(CSSPluginUtilities.pathOf(originalFile), url);
		return CSSPluginUtilities.relativePath(newFile, absoluteUrl);
	});
}