Need to resize video slider to fit width of viewing window

How do I get the video to resize for the width of the screen? I don't want only a portion of the video (center/middle) to show on smaller screens. I would like the entire video to resize like on this site's homepage at top: https://www.anchoandagave.com/. Video and window get smaller proportionately for the viewing width.

Hello??? How do I get the video width to resize to screen width? The video is cutoff on medium/smaller screens.