mail/src/sass/blocks/layout/_app.scss

// Main Application Layout

.app {
    $aside-width:           260px;
    $aside-width-lg:        220px;
    $header-height:         80px;

    position: relative;
    height: 100%;

    // disable text selection
    user-select: none;

    &__aside {
        position: absolute;
        left: 0;
        top: 0;
        height: 100%;
        width: $aside-width;
        background: $color-main;
        color: $color-main-text;
        overflow: auto;
        -webkit-overflow-scrolling: touch;
        @include scrollbar(main);

        // hide scrollbar in webkit
        &::-webkit-scrollbar {
            display: none;
        }

        @include respond-to(not-lg) {
            transform: translateX(-100%);
        }
        @include respond-to(lg) {
            width: $aside-width-lg;
            background: $color-bg;
            color: $color-text;
            @include scrollbar(base);
        }
    }
    &__container {
        position: absolute;
        top: 0;
        left: 0;
        right: 0;
        bottom: 0;

        @include respond-to(not-lg) {
            &:after {
                display: block;
                content: '';
                position: absolute;
                top: 0;
                left: 0;
                background: rgba(0,0,0,0.2);
                width: 100%;
                height: 100%;
                transform: translateX(110%); // translate offscreen
            }
        }
        @include respond-to(lg) {
            left: $aside-width-lg;
        }
    }

    &__header {
        display: none;

        @include respond-to(lg) {
            display: block;
            height: $header-height;
        }
    }
    &__main {
        height: 100%;

        @include respond-to(lg) {
            position: absolute;
            bottom: 0;
            width: 100%;
            height: auto;
            top: $header-height;
            border-top: 1px solid $color-border-light;
            border-left: 1px solid $color-border-light;
        }
    }

    // Modifier to open sidebar
    &--show-aside {
        @include respond-to(not-lg) {
            transform: translateX($aside-width);
            .app__container:after {
                transform: none;
            }
        }
    }

    // Animation
    @include respond-to(not-lg) {
        will-change: transform;
        transform-style: preserve3d;
        transition: transform 0.15s ease-out;
        .app__container:after {
            will-change: transform;
            transform-style: preserve3d;
        }
    }
}