wagtail/client/scss/components/_modals.scss

$zindex-modal-background: 500;

.fade {
    @include transition(opacity 0.15s linear);
    opacity: 0;

    &.in {
        opacity: 1;
    }
}

// Kill the scroll on the body
.modal-open {
    overflow: hidden;

    .content-wrapper {
        transform: none;
    }
}

// Container that the modal scrolls within
.modal {
    box-sizing: border-box;
    display: none;
    overflow: auto;
    overflow-y: scroll;
    position: fixed;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    z-index: $zindex-modal-background;
}

// Shell div to position the modal with bottom padding
.modal-dialog {
    box-sizing: border-box;
    margin-left: auto;
    margin-right: auto;
    padding: 0;
    z-index: ($zindex-modal-background + 10);
    height: 90%;
    width: 85%;

    &:before {
        content: '';
        display: inline-block;
        height: 100%;
        vertical-align: middle;
        margin-right: -0.25em;
    }
}

// Actual modal
.modal-content {
    box-sizing: border-box;
    border-radius: 3px;
    width: 98.7%;
    position: relative;
    background-color: $color-white;
    margin-top: 2em;
    padding-bottom: 3em;
    display: inline-block;
    vertical-align: middle;
    overflow: hidden;
}

// Modal background
.modal-backdrop {
    position: fixed;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    z-index: ($zindex-modal-background - 10);
    background-color: $color-black;

    // Fade for backdrop
    &.fade { opacity: 0; }

    &.in { opacity: 0.5; }
}

.modal .close {
    padding: 0;
    position: absolute;
    width: 50px;
    height: 50px;
    top: 10px;
    right: 10px;
    z-index: 1;
}

// Where all modal content resides
.modal-body {
    position: relative;
    padding-bottom: 2em;

    header {
        padding-left: 2em;
        padding-right: 100px;

        &.tab-merged {
            padding-left: 1.6em;
        }
    }

    .header-title {
        // stylelint-disable-next-line declaration-no-important
        padding-left: 0 !important;
        margin-left: -36px;
    }

    .tab-merged .header-title {
        margin-left: 0;
    }
}

@include media-breakpoint-up(sm) {
    .modal-dialog {
        padding: 0 0 2em $menu-width;
    }

    .modal-body {
        header.tab-merged {
            padding-left: $desktop-nice-padding;
        }
    }
}

@include media-breakpoint-up(xl) {
    .modal-dialog {
        max-width: 100em;
        padding: 0 0 2em;
    }
}