xmpp.chapril.org-conversejs/sass/converse/_controlbox.scss

#conversejs {
    #controlbox {
        #converse-register {
            .button-cancel {
                font-size: 90%;
            }
        }

        .controlbox-pane {
            border-bottom-left-radius: $chatbox-border-radius;
            border-bottom-right-radius: $chatbox-border-radius;
            height: 289px;
            @include calc(height, '100% - #{$controlbox-head-height}');
        }

        .brand-heading-container {
            .brand-heading {
                margin-left: 1em;
            }
        }
    }
}