AssetConverter in app-advanced

Hi all.

Exactly how does AssetConverter work?

For instance, I am theming my app advanced in frontend. I have my directory structure as:

app
- backend
- console
...
- frontend
-- themes
--- myTheme
---- scss
---- css
...
-- web
--- assets
--- css
--- themes
---- myTheme
----- css
...

My intention: convert, with sass, a scss file inside my app/frontend/themes/myTheme/scss directory into app/frontend/web/themes/myTheme/css directory or into app/frontend/themes/myTheme/css directory for later publish.

I’m following this guide to do it. But I don’t have any good results. All my tries finish in an error about not finding any file.

My Asset bundle class is:

class AppAsset extends AssetBundle
{
    public $basePath = '@app/themes/grayscale';
    public $baseUrl = '@web/themes/grayscale';
    public $css = [
        'css/grayscale.scss',
        'vendor/fontawesome-free/css/all.min.css'
    ];
    public $js = [
        'js/grayscale.min.js'
    ];
    public $depends = [
        'yii\web\YiiAsset',
        'yii\bootstrap\BootstrapAsset',
        'yii\bootstrap\BootstrapPluginAsset',
    ];
    
}

I have configured the command option in various modes without successful results:

'commands' => [
      'scss' => ['css', 'sass @app/themes/grayscale/scss/grayscale.scss:@app/themes/grayscale/css/grayscale.css {from}:{to} --source-map']
],

This one:

'commands' => [
       'scss' => ['css', 'sass @app/themes/grayscale/scss/grayscale.scss:@app/themes/grayscale/css/grayscale.css {from} {to} --source-map']

],

This other:

'commands' => [
       'scss' => ['css', 'sass @app/themes/grayscale/scss/grayscale.scss:@webroot/themes/grayscale/css/grayscale.css {from} {to} --source-map']
],

No one works.