wagtail/client/scss/components/_tabs.scss

.tab-nav {
    @include row();
    padding: 0;
    background: $color-grey-4;

    li {
        list-style-type: none;
        width: 33%;
        float: left;
        padding: 0;
        position: relative;
        margin-right: 2px;

        &:first-of-type {
            padding-left: $desktop-nice-padding;
            margin-left: 0;
        }
    }

    h2 {
        margin: 0;
        font-size: inherit;
    }

    a {
        @include transition(border-color 0.2s ease);
        background-color: $color-teal-darker;
        text-transform: uppercase;
        font-weight: 600;
        text-decoration: none;
        display: block;
        padding: 0.6em 0.7em 0.8em;
        color: $color-white;
        border-top: 0.3em solid $color-teal-darker;
        max-height: 1.44em;
        overflow: hidden;

        &:hover {
            color: $color-white;
            border-top-color: rgba(0, 0, 0, 0.35);
        }
    }

    a.errors {
        &:after {
            border-radius: 50px;
            box-shadow: 1px 2px 2px rgba(0, 0, 0, 0.1);
            position: absolute;
            right: -0.5em;
            top: -0.5em;
            z-index: 5;
            min-width: 0.9em;
            color: $color-white;
            background: $color-red;
            content: attr(data-count);
            padding: 0 0.3em;
            line-height: 1.4em;
            text-align: center;
            font-size: 0.8em;
        }
    }

    li.active a {
        box-shadow: none;
        color: $color-grey-1;
        background-color: $color-white;
        border-top: 0.3em solid $color-grey-1;
    }

    // For cases where tab-nav should merge with header
    &.merged {
        margin-top: 0;
        background-color: $color-header-bg;
    }

    li.right {
        float: right;
        margin-right: 0;
        margin-left: 2px;
    }

    li.wide {
        width: unset;
    }

    .right {
        max-height: 1.44em;
        overflow: visible;
    }
}

.tab-content {
    > section {
        display: none;
        padding-top: 1em;

        &.active {
            display: block;
        }
    }

    .page-locked & {
        cursor: not-allowed;
        user-select: none;

        > * {
            pointer-events: none;
        }
    }
}

@include media-breakpoint-up(sm) {
    .tab-nav {
        // For cases where tab-nav should merge with header
        &.merged {
            background-color: $color-header-bg;
        }

        li {
            width: auto;
            padding: 0;
        }

        a {
            padding-left: $mobile-nice-padding;
            padding-right: $mobile-nice-padding;
        }

        li.settings a {
            padding-left: 2em;
            padding-right: 2em;
        }
    }

    .modal-content .tab-nav li {
        padding: 0;
        min-width: 0;

        &:first-of-type {
            padding-left: $desktop-nice-padding;
        }
    }
}

@include media-breakpoint-down(xs) {
    // To allow tabs on the edit page to be editable
    .tab-nav li:first-of-type {
        padding-left: 1.6em;
    }

    .tab-nav li {
        width: auto;
    }
}