Cornea/user_config/usr/share/cornea/stylesheet.css

.region-window {
    background-color: rgba(0, 0, 0, 0.0);
    /* border: 2px solid rgba(136, 204, 39, 1); */
    /* Dark Bergundy */
    border: 2px solid rgba(116, 0, 0, 1);
}

.expand-button {
    background-color: rgba(0, 0, 0, 0.0);
    border: 2px solid rgba(56, 56, 56, 1);
}