:root {
    --card-height: 40vw;
    --card-margin: 4vw;
    --card-top-offset: 1em;
    --numcards: 4;
    --outline-width: 0px;
}

#cards {
    padding-bottom: calc(var(--numcards) * var(--card-top-offset)); /* Make place at bottom, as items will slide to that position*/
    margin-bottom: var(--card-margin); /* Don't include the --card-margin in padding, as that will affect the scroll-timeline*/
}

#card_1 {
    --index: 1;
}

#card_2 {
    --index: 2;
}

#card_3 {
    --index: 3;
}

#card_4 {
    --index: 4;
}

.card {
    position: sticky;
    top: 0;
    padding-top: calc(var(--index) * var(--card-top-offset));
}

@supports (animation-timeline: works) {

    @scroll-timeline cards-element-scrolls-in-body {
        source: selector(body);
        scroll-offsets:
            /* Start when the start edge touches the top of the scrollport */
            selector(#cards) start 1,
            /* End when the start edge touches the start of the scrollport */
            selector(#cards) start 0
        ;
        start: selector(#cards) start 1; /* Start when the start edge touches the top of the scrollport */
        end: selector(#cards) start 0; /* End when the start edge touches the start of the scrollport */
        time-range: 4s;
    }

    .card {
        --index0: calc(var(--index) - 1); /* 0-based index */
        --reverse-index: calc(var(--numcards) - var(--index0)); /* reverse index */
        --reverse-index0: calc(var(--reverse-index) - 1); /* 0-based reverse index */
    }
    
    .card__content {
        transform-origin: 50% 0%;
        will-change: transform;

        --duration: calc(var(--reverse-index0) * 1s);
        --delay: calc(var(--index0) * 1s);

        animation: var(--duration) linear scale var(--delay) forwards;
        animation-timeline: cards-element-scrolls-in-body;
    }

    @keyframes scale {
        to {
            transform:
                scale(calc(
                    1.1
                    - 
                    calc(0.1 * var(--reverse-index))
                ));
        }
    }
}

/** DEBUG **/

#debug {
  position: fixed;
  top: 1em;
  left: 1em;
}
#debug::after {
  content: " Show Debug";
  margin-left: 1.5em;
  color: white;
  white-space: nowrap;
}

#debug:checked ~ main {
  --outline-width: 1px;
}

/** PAGE STYLING **/

* { /* Poor Man's Reset */
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

main {
    width: 50vw;
    margin: 0 auto;
}

@media (max-width: 768px) {
    main {
        width: 90vw;
    }
    .card {
        padding-top: 0;
    }
    .card__content {
        grid-template-areas: "img" "text";
        grid-template-columns: 1fr;
        grid-template-rows: auto auto;
    }
    :root {
        --card-height: 80vw; /* Increase card height for mobile */
    }
}

#cards {
    list-style: none;
    outline: calc(var(--outline-width) * 10) solid blue;
    
    display: grid;
    grid-template-columns: 1fr;
    grid-template-rows: repeat(var(--numcards), var(--card-height));
    gap: var(--card-margin);
}

.card {
    outline: var(--outline-width) solid hotpink;
}

.card__content {
    box-shadow: 0 0.2em 1em rgba(0, 0, 0, 0.1), 0 1em 2em rgba(0, 0, 0, 0.1);
    background: rgba(255, 255, 255,0);
    color: rgb(10, 5, 7);
    border-radius: 1em;
    overflow: hidden;

    display: grid;
    grid-template-areas: "text img";
    grid-template-columns: 1fr 1fr;
    grid-template-rows: auto;

    align-items: stretch;
    outline: var(--outline-width) solid lime;
}

.card__content > div {
    grid-area: text;
    width: 80%;
    place-self: center;
    text-align: left;

    display: grid;
    gap: 1em;
    place-items: start;
}

.card__content > figure {
    grid-area: img;
    overflow: hidden;
}

.card__content > figure > img {
    width: 100%;
    height: 100%;
    object-fit: cover;
}