Userstyle to minimize the empty space in tlk.io's desktop view, also hides header avatar.

tlk.io.userstyle.css

/* hide the header avatar */
.header-avatar {
    background: inherit !important;
    pointer-events: none;
    cursor: default;
}

/* wide desktop view */
@media (min-width: 761px) {
    /* move the online list to the side */
    .aside {
        right: 14px;
        margin-left: unset !important;
        left: unset !important;
    }

    /* make the chat wider */
    .chat {
        width: 100%;
    }

    /* make the message input wider */
    .footer-wrapper {
        width: calc(100% - 100px);
    }
}

/* extra breakpoint to match input to the message width */
@media (min-width: 920px) {
    .footer-wrapper {
        width: calc(100% - 300px);
    }
}