Custom Styles not applied when in fullscreen mode

[BridgingUnit]

Description

Custom Styles added under Advanced settings in CKEditor field settings don't seem to be applied when editor is in fullscreen mode

Steps to reproduce

1. Create a CKEditor field with headings enabled
2. In same settings include button for fullscreen mode
3. Under Advanced add Custom Styles either via CSS or file set to something like

.ck.ck-content h2 {	
font-size: 1.4rem !important;
font-weight: normal !important;
}

4. In Entry where that field is applied, add some sample text, select part of that, and apply Heading 2 styles from dropdown in menu - you should see the size of that heading change with the editor in the field in situ.
5. Click fullscreen mode button in field menu bar
6. Those custom styles disappear and revert back to default CKEditor styles.

Additional info

• Craft version: 5.10.7
• PHP version: 8.3.32
• Database driver & version: MySQL 8.0.46
• Plugins & versions: CKEditor 5.6.1

[linear-code]

PT-3409

[i-just]

Hi, thanks for reporting! I raised a PR for this.