wagtail/client/scss/components/_help-block.scss

// Help text formatters
.help-block {
    padding: 1em;
    margin: 1em 0;
    clear: both;
    color: $color-text-base;

    p {
        margin-top: 0;

        &:last-child {
            margin-bottom: 0;
        }
    }

    a {
        color: $color-link;
    }
}

.help-info,
.help-warning,
.help-critical {
    border-radius: 3px;
    padding-left: 3.5em;
    position: relative;

    &:before {
        font-family: wagtail;
        position: absolute;
        left: 1em;
        top: 0.7em;
        content: '?';
        font-size: 1.4em;
    }
}

.help-info {
    background-color: lighten($color-blue, 30%);

    &:before {
        color: $color-blue;
    }
}

.help-warning {
    background-color: lighten($color-orange, 30%);

    &:before {
        color: $color-orange;
        content: '!';
    }
}

.help-critical {
    background-color: lighten($color-red, 40%);

    &:before {
        color: $color-red;
        content: '!';
    }
}