findCssImports(chunk, imports = []) {
		for (const f of chunk.referencedFiles) {
			if (isCssFilename(f) && !imports.includes(f)) imports.push(f);
		}
		for (const child of chunk.imports) {
			const c = this.bundle[child];
			if (c) this.findCssImports(c, imports);
		}
		return imports;
	}
Get the CSS asset fileNames referenced by a chunk and its statically-imported children.
@param {Chunk} chunk
@param {string[]} [imports]