jellyfin-web/dashboard-ui/css/polymer/paper-icon-button-light.css

[is=paper-icon-button-light] {
    width: 40px;
    height: 40px;
    padding: 8px;
}

    [is=paper-icon-button-light] iron-icon, [is=paper-icon-button-light] img {
        /* Don't specify both dimensions or it may not get sized properly */
        /*width: 100%;*/
        height: 100%;
    }

    [is=paper-icon-button-light] #background {
        transition: opacity .3s ease-out;
    }

    [is=paper-icon-button-light]:focus #background {
        background-color: currentcolor !important;
        opacity: .2 !important;
    }