inject.css

.only-chat div.bc-chat-container,
.only-chat div.bc-chat-container > div.inner {
    background: white;
    bottom: 0;
    left: 0;
    right: 0;
    top: 0;
    position: fixed;
    width: 100%;
    z-index: 5000000;
}

.only-chat .chat-activity.chat-message .inner {
    width: inherit;
}

.only-chat #header-container,
.only-chat #player-wrapper,
.only-chat #sidebar,
.only-chat #bc-share  {
    display:none !important;
}

button#toogleChatButton {
    right: 0;
    top: 0;
    position: fixed;
    z-index: 10000000;
}