Steps to reproduce:

• Go to a course
• Add a "Text and media" element
• Add a larger amount of content to the TinyMCE text editor
• Switch to the source code view in TinyMCE

Expected result:

• The HTML source code is shown
• The HTML source code is longer than the source code area's viewport
• The source code area has one vertical scrollbar

Actual result:

• The HTML source code is shown
• The HTML source code is longer than the source code area's viewport
• The source code area has two vertical scrollbars

Notes:

• The issue could be reproduced in Chrome and Edge, but not in Firefox
• The correct styling for the .modal-codemirror-container element would be "overflow: auto;" to avoid this issue. However, you can't set this style as hotfix in your theme as this is a #shadow-root element unfortunately.