youtube-chat.css

#items { overflow: hidden !important; }
*:not(.yt-chat-badge):not(.yt-emoji-icon) { background: transparent !important; }
.gaming-promo, #live-comments-controls, ::-webkit-scrollbar, wbr, .is-deleted, [is-deleted], #panel-pages, yt-live-chat-header-renderer { display: none !important; }
#author-name, #message { color: white !important; text-shadow: -0.5px -0.5px 0 black, 0.5px -0.5px 0 black, -0.5px 0.5px 0 black, 0.5px 0.5px 0 black !important; }
#message { display: block !important; }
#author-name::after { content: ":"; font-weight: 900; }
#message a {color: skyblue !important; font-size: 0 !important; line-height: 9px !important;}
#message a::after { content: attr(href); font-size: 10px !important; }
@keyframes chat-fade { 0% { opacity: 1; position: relative; } 99% { opacity: 0; position: relative; } 100% { opacity: 0; position: absolute; }}
yt-live-chat-text-message-renderer { animation: chat-fade 5s 30s forwards; }
/* #author-photo { border-radius: 10px !important; } */

Seems that youtube added a reminder that won't go away

Just ad yt-live-chat-viewer-engagement-message-renderer { visibility: hidden; } and it will go away