A screenshot of Vivaldi with floating tabs and some additional whitespace to the right.

1. Visit vivaldi://experiments and tick the "Allow for CSS modifications" box.
2. Then go to: vivaldi://settings/appearance/ and choose a folder to load from. (Place the new CSS there or choose the folder, where you cloned the repository to.)
3. Restart Vivaldi

For more informations head over to:
https://forum.vivaldi.net/topic/37802/css-modifications-experimental-feature

Modification of the Vivaldi light them. You can simply import this theme-file: download theme

There is a nice transition when activating a tab or hovering over it and you will probably notice haveing a pointer cursor.

It also supports highlighting of background-audio, if the audio is not playing in the active tab:

There is also a custom icon for macOS, you can apply to Vivaldi, in cas you want a slightly cleaner lookin icon. The icon is taken from: https://de.wikipedia.org/wiki/Datei:Vivaldi_web_browser_logo.svg

I then scale it up a bit, so that it matches the other macOS-Icons (in size and shape).

1. Find Vivaldi in the Applications-folder in the finder
2. right-click, the Vivald.app and slect Informations
3. Drage the icon over to the icon in the upper left area of the new window.
4. restart Vivaldi and the new icon is applied.

If you want to remove that icon again, simply follow the preocedure from above, but instead of adding a new icon, just delete it.

⚠️ You have to reapply the icon after each update of Vivaldi