style.css

:focus {
  outline: 4px solid red;
}

.dark-mode-on ytd-rich-grid-video-renderer:focus {
  background: #fff;
  margin-top: -0.25rem;
}

.dark-mode-on ytd-rich-grid-video-renderer:focus #video-title {
  color: #000 !important;
}

.dark-mode-on ytd-rich-grid-video-renderer:focus yt-formatted-string[has-link-only_]:not([force-default-style]) .style-scope {
  color: #5d5d5d !important;
}

.dark-mode-off ytd-grid-video-renderer,
.dark-mode-off ytd-compact-video-renderer,
.dark-mode-off ytd-video-renderer,
.dark-mode-off ytd-rich-grid-video-renderer {
  opacity: 0.75;
}

.dark-mode-off ytd-rich-grid-video-renderer:focus {
  margin-top: -0.25rem;
}

.dark-mode-off :focus {
  opacity: 1;
}

.ytd-shelf-renderer ytd-grid-video-renderer:focus {
  padding-right: 0 !important;
}

#items.yt-horizontal-list-renderer ytd-grid-video-renderer:focus {
  margin-right: 4px;
}