Issues with RTE because of contentsCss

# Bug Report

## Prerequisites

* [x] Can you reproduce the problem on TYPO3 v9.5 LTS
* [x] Can you reproduce the problem on TYPO3 v10.4 LTS
* [x] Did you [perform a cursory search](https://github.com/issues?q=is%3Aissue+user%3Abenjaminkott+repo%3Abenjaminkott%2Fbootstrap_package)
to see if your bug or enhancement is already reported?

## Description

I've found some issues and "hipcups" with the CSS which was used for ckeditor.

1) Buttons are not clickable, the text can't be changed. To reproduce, click on third button and try to change the text:


2) The default text size is pretty high: the text size is higher than the other texts in the TYPO3 BE or the buttons of the RTE (compare it to button "Normal").


3) There's so much unneeded CSS code in bootstrapX-rte.css, e.g. for PhotoSwipe or carousel. This should be removed.

## How to fix

Change the styles in EXT:bootstrap_package/Resources/Public/Css/bootstrapX-rte(.min).css.
I will provide a PR.