jellyfin-web/dashboard-ui/css/notifications.css

.btnNotifications {
    text-decoration: none !important;
    outline: 0 !important;
    vertical-align: middle;
    width: auto;
    margin: 0;
    padding-top: 0;
    padding-bottom: 0;
}

.btnNotificationsInner {
    color: #fff;
    font-weight: 500;
    position: relative;
    border-radius: 1000px;
    background: #444;
    line-height: 28px;
    min-width: 30px;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    text-align: center;
}

.levelNormal {
    background-color: #43A047;
}

.levelWarning {
    background-color: #FF7537;
}

.levelError {
    background-color: #d14836;
}

.flyoutNotification {
    border-top: 1px solid #404040;
    padding: 0 0 .5em;
}

    .flyoutNotification p {
        margin: .5em 0;
        white-space: normal;
        max-width: 95%;
    }

    .flyoutNotification:last-child {
        border-bottom: 1px solid #404040;
    }

    .flyoutNotification a {
        font-weight: 500 !important;
    }

.notificationTime {
    color: #52B54B;
}

.notificationImage {
    margin: 0 .5em 0 1em;
    padding: .5em 0;
    display: inline-block;
    vertical-align: top;
    display: none;
}

.notificationContent {
    display: inline-block;
    vertical-align: top;
    overflow: hidden;
}

.unreadFlyoutNotification {
    color: blue;
}

.imgNotification, .imgNotificationInner {
    width: 40px;
    height: 40px;
}

.imgNotificationInner {
    background-repeat: no-repeat;
    background-size: contain;
    background-position: center center;
}

.imgNotificationNormal {
    background-color: #4d90fe;
    background-image: -webkit-gradient(linear,left top,left bottom,from(#4d90fe),to(#4787ed));
    background-image: -webkit-linear-gradient(top,#4d90fe,#4787ed);
    background-image: -moz-linear-gradient(top,#4d90fe,#4787ed);
    background-image: -ms-linear-gradient(top,#4d90fe,#4787ed);
    background-image: -o-linear-gradient(top,#4d90fe,#4787ed);
    background-image: linear-gradient(top,#4d90fe,#4787ed);
}

.imgNotificationError {
    background-color: #d14836;
    background-image: -webkit-gradient(linear,left top,left bottom,from(#dd4b39),to(#d14836));
    background-image: -webkit-linear-gradient(top,#dd4b39,#d14836);
    background-image: -moz-linear-gradient(top,#dd4b39,#d14836);
    background-image: -ms-linear-gradient(top,#dd4b39,#d14836);
    background-image: -o-linear-gradient(top,#dd4b39,#d14836);
    background-image: linear-gradient(top,#dd4b39,#d14836);
}

.imgNotificationWarning {
    background-color: #FF7537;
}