grunt: uglify css files with uglifyjs

I'm using grunt to uglify my static files (using grunt v0.4.0). I have configured it to uglify one file, but I can't figure out how to get it to do two files - despite reading this question and the usage examples. Here's what I have currently: ``` uglify: { options: { banner: '/*! <%= pkg.name %> <%= grunt.template.today("yyyy-mm-dd") %> */\n', mangle: true }, build: { src: 'dist/main.js', dest: 'dist/main.min.js' } } ``` I'd like to uglify `dist/main.css` as well. How can I add it? I tried this, following the usage examples: ``` uglify: { options: { banner: '/*! <%= pkg.name %> <%= grunt.template.today("yyyy-mm-dd") %> */\n', mangle: true }, build: { files: { 'dist/main.min.js': ['dist/main.js'], 'dist/main.min.css': ['dist/main.css'] } } } ``` But this gives me the following error: ``` WARN: ERROR: Unexpected token: punc ({) [dist/main.css:7,41] Warning: Uglification failed. Use --force to continue. Aborted due to warnings. ``` Seems like it's choking on the first `{` - why would that happen? It is valid CSS.