If you have changed the background color of the file explorer container that lists your files, you may also want to change the background color of the top bar with the tabs.
I have added the code for that to the repository. You can find it in the chapter “File explorer - Obsidian”, section “Top tab container background color”.
I have also added code how to change the background color of a note spine in Andy mode. Check out chapter “Note title in pane”, then “Change color of note spine (Andy mode)”.
The link to the repository is given in the OP at the top of this page.
Both sets of codes are thanks to @Lithou. You can see his explanations (nos. 1 and 2 in the list) on YouTube; there are a few other useful CSS issues he deals with.
Enjoy.