styles.css

/* Define styles for the chat area */
body, yt-live-chat-renderer, yt-live-chat-item-list-renderer {
    background-color: transparent !important;
    margin: 0 !important;
    overflow: hidden !important;
    width: 100% !important;
    height: 100% !important;
}

/* Adjusts message area height and defines positioning */
yt-live-chat-item-list-renderer {
    position: absolute;
    bottom: 20px;
    height: calc(100% - 40px) !important;
    padding: 0 10px !important;
    box-sizing: border-box !important;
}

/* Styles for messages and owner author color */
yt-live-chat-text-message-renderer {
    background-color: transparent !important;
    width: calc(100% - 20px) !important;
    margin: 5px 0 !important;
    padding: 0 !important;
    font-size: 14px !important;
    color: #fff !important;
    white-space: pre-wrap !important;
}

/* Owner author color */
yt-live-chat-text-message-renderer.yt-live-chat-text-message-author-is-owner #author-name {
    color: #000 !important;
}

/* Removes unnecessary elements and notices */
#header, #primary-content, #secondary-content, #footer,
yt-live-chat-header-renderer, yt-live-chat-message-input-renderer,
yt-live-chat-action-panel-renderer, yt-live-chat-message-prompt-renderer,
yt-live-chat-viewer-engagement-message-renderer,
yt-live-chat-text-message-renderer #img, ::-webkit-scrollbar,
yt-live-chat-membership-only-mode-message-renderer,
yt-live-chat-mode-change-message-renderer,
yt-live-chat-restricted-participation-renderer,
yt-live-chat-author-chip-renderer,
yt-live-chat-legacy-paid-message-renderer,
yt-live-chat-legacy-paid-sticker-renderer,
yt-live-chat-pinned-message-renderer,
yt-live-chat-viewer-engagement-message-renderer,
yt-live-chat-text-message-renderer yt-icon,
yt-live-chat-renderer #input, yt-live-chat-text-message-renderer yt-live-chat-author-chip-renderer,
yt-live-chat-subscription-message-renderer,
yt-live-chat-paid-message-renderer,
yt-live-chat-paid-sticker-renderer,
yt-live-chat-restricted-participation-renderer {
    display: none !important;
}