My youtube CSS

.watch-sidebar,
.watch-main-col,
body #footer-container,
#masthead-positioner,
#masthead-positioner-height-offset,
.ytp-ce-covering-overlay,
.ytp-endscreen-content,
.ytp-button.ytp-endscreen-previous,
.ytp-button.ytp-endscreen-next
{
    display: none;
}

.ytp-chrome-bottom {
    position: fixed;
    top: 0;
    left: 0;
}

.ytp-player-content.ytp-iv-player-content,
.video-stream.html5-main-video,
#placeholder-player
{
    display: none;
}

.player-height {
    height: 40px;
}

/* ytp-controls alway show
https://greasyfork.org/en/forum/discussion/4304/disable-auto-hide-progress-bar-and-controls
*/
.ytp-autohide:not(.ytp-watch-controls) .ytp-chrome-bottom,
.ytp-chrome-bottom[aria-hidden=true] {
    opacity: 1;
}