qwc2/plugins/style/ThemeSwitcher.css

QGIS Web Client

div.theme-switcher-filter {
    flex: 100 1 auto;
    max-width: 15em;
    font-weight: normal;
    color: var(--text-color);
    margin: 0 0.5em;
}

div.active-theme {
    order: 0;
}