Steps to reproduce
1. Make sure to use ckeditor_classic in the web content creation page, by setting the following property
2. In some site, go to the web content creation page and create a "Basic Web Content"
Checkpoint: you should see the ckeditor classic, with a toolbar where a "Video" button is available right before "Source" mode button:
There are 2 visual glitches in this button.
- Button has a different styling from the other ones: it's black rather than dark grey, it seems taken from a different button set
- In "Source" mode, button is not greyed-out. This gives the impresion it's still clickable when it is not
- Button has a similar style as the others, in particular, its color
- In "Source" mode, button is greyed out
Video button seems to be the ootb one provided by ckeditor plugin. A quick check to the styling reveals that, as opposed to the other buttons in the bar, it's not being provided by editor.css