Need help to embed 21:9 video responsively

Hi, I am using a responsive theme and have had limited success trying to embed a vimeo video responsively on the front page.
It’s a 21:9 aspect ratio video and so far I’ve only been able to get 16:9 ‘containers’ in the css coding I’ve found (online) which leaves black bars either side of the video…not what I want!
I want it to fill the entire top of the page - no gaps on the top, bottom or sides.
Does anyone know of some customisable coding or even a stack add-on that’ll do the job?

Many thanks in advance…