不能得到咕的uglify来处理js或css文件

Question

我正在尝试创建一个gruntfile来对我的js和css文件进行编译，但是我一直收到错误Warning: Required config property "uglify.css" missing. Use --force to continue.所有其他grunt任务都可以正常工作，只是grunt-contrib-uglify似乎可以抛出错误。

这是我的文件夹结构：

这是我的Gruntfile.js：

module.exports = function(grunt) {


grunt.initConfig({
    autoprefixer: {
        dist:{
            files:{
                'css/theme.scss':'css/theme.scss'
            }
        }
    },
    sass: {
        dist: {
            files: {
                'css/theme.css':'css/theme.scss'
            }
        }
    },
    concat: {
       js: {
            src: ['js/jquery-3.3.1.slim.min.js', 'js/popper.min.js', 'js/bootstrap.js', 'js/scripts.js'],
            dest: 'dist/js/scripts.js',
        },
        css: {
            src: ['css/bootstrap.css', 'css/theme.css'],
            dest: 'dist/css/styles.css',
        },
    },
    uglify: {
        dist: {
            css: {
                'dist/css/styles.min.css': ['dist/css/styles.css'],
            },
            js: {
                'dist/js/scripts.js': ['dist/js/scripts.js'],
            }
        }
    },
    watch: {
        prefixer: {
            files: 'css/**/*.css',
            tasks: ['autoprefixer'],
        },
        sass: {
            files: 'css/**/*.scss',
            tasks: ['sass'],
        },
        js: {
            files: 'js/**/*.js',
            tasks: ['concat:js'],
        },
        css: {
            files: 'css/**/*.css',
            tasks: ['concat:css'],
        },
        uglifyCss: {
            files: 'css/**/*.css',
            tasks: ['uglify:css'],
        },
        uglifyJs: {
            files: 'js/**/*.js',
            tasks: ['uglify:js'],
        },
    },
});


grunt.loadNpmTasks('grunt-autoprefixer');
grunt.loadNpmTasks('grunt-contrib-sass');
grunt.loadNpmTasks('grunt-contrib-concat');
grunt.loadNpmTasks('grunt-contrib-uglify');
grunt.loadNpmTasks('grunt-contrib-watch');

};  

不确定我在这里做错了什么，我们将提供任何帮助。谢谢！