Overriding styles

How do i override vaadin tabs style and customize it ?

if you need to customize the default vaadin styles you can do it in your theme file. (If you have created an application from archetype, than the file will be called mytheme.sccs). For example, if you want to modify the background of the tab, you can inspect the right name to be used in developer tools and then set background: yourColor in the theme folder.
I will attach an example from the developer tools used for TabSheet. You can add the line added there directy to there theme file, recompile the theme and effect should be the same.

Hopefully it helps : )