Need my Video to stop resizing on loading the page

Using custom code I have been able to round the corners of videos on my site, as I don't want them to be square. 

I'm using this: 

.video-player .plyr video {
    object-fit: cover !important;
    border-radius: 10px !important;
}

But every time I load the page the video keeps glitching by defaulting to the original square layout for a second and then resizing to the rounded version. 

Is there any CSS code I could try to stop this from happening? So that the video doesn't readjust every time, I refresh. 

Can you share link to page where you use video? We can check easier