[🚩css export]: make primary css-export pure CSS (CSS variables)

[ala-n]

As an ESL consumer, I want to be able to have ESL modules CSS export configurable.

Scope

In the bounds of the epic esl modules styles primary export became CSS. All style customizations should be handled with CSS variables. ESL Tag customization feature from that moment is not officially supported for all ESL modules.

Priority High

Modules

• [ ] esl-alert
• [ ] esl-animate (most likely will be covered in bounds of ^4.8.* versions)
• [ ] esl-footnotes
• [ ] esl-select
• [ ] esl-select-list
• [ ] esl-image
• [x] esl-panel
• [x] esl-panel-group
• [ ] esl-popup
• [ ] esl-scrollbar
• [ ] esl-share
• [ ] esl-tab
• [x] esl-tooltip

Additional Notes

• Investigate for the most smooth transition without a significant break of the current less and CSS assets export