How to compress css file?

Question

Yii

I don’t understand a little how to make css like min.css. I tried to use asset manager but for some reason it didn't work
for me I already have the configuration in frontend/config/main.php

'assetManager' => [
            'bundles' => [
                'yii\web\JqueryAsset' => [
                    'sourcePath' => null,
                    'js' => [
                        '//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js'
                    ]
                ],
                'yii\bootstrap\BootstrapPluginAsset' => [
                    'sourcePath' => null,
                    'js' => [
                        'https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js'
                    ]
                ],
                'yii\bootstrap\BootstrapAsset' => [
                    'sourcePath' => null,
                    'css' => [
                        'https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css'
                    ]
                ]
            ],
            'appendTimestamp' => true
        ],

I did this by minifying the jquery and bootstrap libraries.
When I specified yii asset/template assets.php in the console, the file was created in the root folder
. And when I try to run compress or config, I get an error all the time. For compress Error: ╨░╤А╨│╤Г╨╝╨╡╨╜╤В╤L: bundleFile
A for config Exception 'yii\base\InvalidConfigException' with message 'The directory does not exist: C:\OpenServer\domains\crm/. ./web/assets'
Although there is a directory in principle. Help deal with this