center container vertical

Hi to all,

is it possible to vertical align a video?
Onclick the video-container is allways on top!

I’ve tried:
@media only screen and (max-width:320px){
.arve-wrapper {
margin-top: 50%;
}
}
and so on…for each device size…which works with Firebug, but not when I write it into the CSS file.

Am I doing anything wrong?
Maybe you now better how to fix it…or…is it actually possible?

Thank you.

https://ww.wp.xz.cn/plugins/advanced-responsive-video-embedder/