OBS chat CSS

obs-chat-overlay.css

html { background-color: transparent !important; }
body { background-color: transparent !important; margin: 0px auto; overflow: hidden; }

/* BEGIN YOUTUBE */

yt-live-chat-renderer,
#items.yt-live-chat-item-list-renderer > .yt-live-chat-item-list-renderer {
  background-color: transparent;
}

yt-live-chat-app,
#contents.yt-live-chat-app,
yt-live-chat-renderer {
  min-height: auto !important;
}

#items yt-live-chat-text-message-renderer > #content,
ytd-sponsorships-live-chat-gift-redemption-announcement-renderer > #content {
  //width: 100%;
  background-color: rgb(255,255,187);
  padding: 4px;
  border: 2px ridge #d3d7cf;
  //border: 2px solid #888a85;
  border-radius: 4px;
  box-shadow: 4px 4px 4px 0 #55575380;
}

#panel-pages,
yt-live-chat-header-renderer,
yt-live-chat-viewer-engagement-message-renderer,
yt-img-shadow,
#ticker {
  display: none !important;
}
yt-live-chat-text-message-renderer {
  font-size: 20px;
  padding: 4px 8px;
}

#visible-banners yt-live-chat-banner-renderer #header {
  display: none !important;
}
#visible-banners yt-live-chat-banner-renderer #contents {
  height: auto !important;
  transform: translateY(0px) !important;
}
#visible-banners yt-live-chat-banner-renderer yt-live-chat-text-message-renderer #content.yt-live-chat-text-message-renderer {
  font-size: 0.9em !important;
}
yt-live-chat-text-message-renderer[in-collapsed-banner] #content.yt-live-chat-text-message-renderer {
  white-space: inherit !important;
  overflow: inherit !important;
}
yt-live-chat-text-message-renderer[in-banner] {
  padding: 4px !important;
}
yt-live-chat-banner-manager[has-active-banner] {
  background: none !important;
}

#live-chat-item-list-panel > #contents > #item-scroller {
  scrollbar-width: none !important;
}

yt-live-chat-renderer[has-action-panel-renderer] #action-panel.yt-live-chat-renderer {
  bottom: unset;
  top: 0;
  right: unset;
  padding: 0;
}
yt-live-chat-poll-header-renderer,
#content.yt-live-chat-poll-choice {
  /*font-size: 0.9em;*/
  padding: 2px;
}

#reaction-control-panel {
  display: none;
}

/* END YOUTUBE */

/* BEGIN TWITCH */

#root .chat-room {
  background: none;
  background-color: transparent;
}

#root .stream-chat-header,
#root .chat-room__content > div:first-child,
#root .chat-input,
#root .chat-line__status[data-a-target="chat-welcome-message"] {
  display: none !important;
}

#root .scrollable-area[data-a-target="chat-scroller"] {
  scrollbar-width: none !important;
}
#root .scrollable-area[data-a-target="chat-scroller"] .simplebar-track {
  display: none !important;
}

#root .chat-line__message {
  font-size: 18px;
  background-color: rgb(255,255,187);
  padding: 8px;
  border: 2px ridge #d3d7cf;
  border-radius: 4px;
  box-shadow: 4px 4px 4px 0 #55575380;
  margin: 8px;
}

/* END TWITCH */

obs-chat-window.css

body { background-color: rgba(0, 0, 0, 0); margin: 0px auto; overflow: hidden; }

/* BEGIN YOUTUBE */

yt-live-chat-app,
#contents.yt-live-chat-app,
yt-live-chat-renderer {
  min-height: auto !important;
}

#panel-pages,
yt-live-chat-header-renderer,
yt-live-chat-viewer-engagement-message-renderer,
yt-img-shadow,
#ticker {
  display: none !important;
}
yt-live-chat-text-message-renderer {
  font-size: 18px;
  padding: 4px 8px;
}

#visible-banners yt-live-chat-banner-renderer #header {
  display: none !important;
}
#visible-banners yt-live-chat-banner-renderer #contents {
  height: auto !important;
  transform: translateY(0px) !important;
}
#visible-banners yt-live-chat-banner-renderer yt-live-chat-text-message-renderer #content.yt-live-chat-text-message-renderer {
  font-size: 0.9em !important;
}
yt-live-chat-text-message-renderer[in-collapsed-banner] #content.yt-live-chat-text-message-renderer {
  white-space: inherit !important;
  overflow: inherit !important;
}
yt-live-chat-text-message-renderer[in-banner] {
  padding: 4px !important;
}

#live-chat-item-list-panel > #contents > #item-scroller {
  scrollbar-width: none !important;
}

yt-live-chat-renderer[has-action-panel-renderer] #action-panel.yt-live-chat-renderer {
  bottom: unset;
  top: 0;
  right: 0;
  padding: 0;
}
yt-live-chat-poll-header-renderer,
#content.yt-live-chat-poll-choice {
  /*font-size: 0.9em;*/
  padding: 2px;
}

#reaction-control-panel {
  display: none;
}

/* END YOUTUBE */

/* BEGIN TWITCH */

#root .stream-chat-header,
#root .chat-room__content > div:first-child,
#root .chat-input,
#root .chat-line__status[data-a-target="chat-welcome-message"] {
  display: none !important;
}

#root .scrollable-area[data-a-target="chat-scroller"] {
  scrollbar-width: none !important;
}
#root .scrollable-area[data-a-target="chat-scroller"] .simplebar-track {
  display: none !important;
}

#root .chat-line__message {
  font-size: 18px;
  padding: 6px 8px;
}

/* END TWITCH */

Licensed under the 0BSD:

BSD Zero Clause License

Copyright (c) 2023-2024 Penbu <penbu@penbuvt.ca>

Permission to use, copy, modify, and/or distribute this software for any
purpose with or without fee is hereby granted.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
PERFORMANCE OF THIS SOFTWARE.