2 Interviews:
1st - Describing previous experiences and try to understand the profile.
2nd - Technical questions, verbal, some of them tricky, fun and css test.
For the senior frontend position, they do questions about the new trends in javascript, best practices, explain and decompose a concept that I know very well. In my case I spoke about redux, and the differences between redux, flux and mvc.
Careful, you have to know what you're talking about, my interviewer knew many of those concepts.
Also the second interview was more verbal, questions about the Array.prototype, how to iterate to map, filter, reduce are basic. CSS was simple, so if you think CSS is your expertise that will be easy.
If you have an angular background they make you explain angular terms, like services, controllers, modules, directives.