New content styles are not organized compared to the previous one

[pomek]

📝 Provide detailed reproduction steps (if any)

Let's use the following content styles as an example: https://ckeditor.com/docs/ckeditor5/44.1.0/getting-started/legacy/advanced/content-styles.html

Its structure is presented as follows:

• Header

  /*
   * CKEditor 5 (v44.1.0) content styles.
   * Generated on Tue, 07 Jan 2025 11:59:17 GMT.
   * For more information, check out https://ckeditor.com/docs/ckeditor5/latest/installation/legacy/advanced/content-styles.html
   */

• Variable definitions

  :root {
    /* ... */
  }

• Selector definitions

  .ck-content ... {
    /* ... */
  }

• At-rule definitions

  @media ... {
    /* ... */
  }

Then, let's see how the new content styles look. Example: https://cdn.ckeditor.com/ckeditor5/44.1.0/ckeditor5-content.css

• License header could contain a link to guide what it is (e.g., https://ckeditor.com/docs/ckeditor5/latest/getting-started/setup/css.html).
• Variables, selectors, and at-rules are mixed in an order defined in source files.

Random thoughts

• I would expect that variables are merged and, perhaps, at-rules grouped in a single place. As for the latter, we need to verify if it does not change its semantics.
• Let's update a license header to include the documentation URL. This change does not change much but gives a user a hint as to why it is used.
• The old content styles are not complete. They lack premium features styles (https://cdn.ckeditor.com/ckeditor5-premium-features/44.1.0/ckeditor5-premium-features-content.css).