wagtail/client/scss/components/_messages.capability.scss

.capabilitymessage {
    display: block;
    background-color: $color-red;
    color: $color-white;
    padding: 1em 2em;
    margin: 0;
    position: relative;
    text-align: center;

    a {
        color: $color-white;
        text-decoration: underline;
    }
}