Thanks for your generosity, I'll post it in the modding section. I tried the css you provided but it didn't work. I saved it as css, enabled using css in Vivaldi Experimental and set the folder where the css was in settiings > appearance, custom UI modifications.
Yes, I'm aware of this, but I prefer using the tab bar because the hotkeys for moving tabs (I use the 'h' and 'l' keys on my keyboard) correspond with the actual movement direction. While Microsoft Edge has this feature on Windows, it doesn’t allow you to change the tab name font, which is why I prefer not to use it.