wallabag/themes/baggy/css/messages.css

.messages.error {
    border: 1px solid #c42608;
    color: #c00 !important;
    background: #fff0ef;
    text-align: left;
}

.messages.notice {
    border: 1px solid #ebcd41;
    color: #000;
    background: #fffcd3;
    text-align: left;
}

.messages.success {
    border: 1px solid #6dc70c;
    background: #e0fbcc;
    text-align: left;
}