main.css

:root {
    --color: #000;
    --card-bg: #FFF;
    --colorlight: rgba(102, 103, 99, 0.8);
    /* Olympic guideline says : Ring radius = 12 x stroke width - source : https://stillmed.olympics.com/media/Documents/International-Olympic-Committee/Olympic-brand/Olympic-Brand-Guidelines.pdf */
    --stroke: 1.4rem;
    --ring1: #0078D0;
    --ring2: #FFB114;
    --ring3: #000000;
    --ring4: #00A651;
    --ring5: #F0282D;
}

html, body {
    font-family: "Manrope", sans-serif;
    min-height: 100vh;
    font-weight: 500;
    color: var(--color);
}

body {
    overflow: hidden;
    background:
            linear-gradient(
                    rgba(0, 0, 0, .65),
                    rgba(0, 0, 0, .65)
            ),
            url(./images/poster.avif) center center / cover no-repeat,
            linear-gradient(135deg,#9bc8c5, #f6ead2,#a2deaa);
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
}

h1 {
    font-size: 2rem;
}

a {
    text-decoration: underline;
    transition: .3s;
}

a:hover {
    color: #000;
}

aside {
    color: var(--colorlight);
    font-size: 0.9rem;
    display: flex;
    flex-direction: column;
    gap: .5rem;
}

.card {
    gap: 1rem;
    padding: 1rem;
    background: #FFF;
    width: calc(100% - 5rem);
    max-width: 1440px;
    height: calc(100vh - 2rem);
    max-height: 770px;
    display: flex;
    flex-direction: column;
    justify-content: space-evenly;
    /* https://shadows.brumm.af/ */
    box-shadow:
            0px 0px 1.3px rgba(0, 0, 0, 0.024),
            0px 0px 3.6px rgba(0, 0, 0, 0.035),
            0px 0px 8.7px rgba(0, 0, 0, 0.046),
            0px 0px 29px rgba(0, 0, 0, 0.07)
    ;
}

.methodology {
    font-size: .8em;
}

/** Continents **/
.continents {
    display: grid;
    grid-template-columns: repeat(3, calc(12 * var(--stroke)));
    justify-content: center;
    gap: calc(var(--stroke));
}

.continent {
    width: calc(12 * var(--stroke));
    display: flex;
    flex-direction: column;
    grid-row: 1/ span 1;
    grid-column: 1 / span 1;
    gap: 1.5rem;
    --header-offset: calc(1.5rem + 52px);
}

.continent header {
    height: 52px;
    display: flex;
    flex-direction: column;
    gap: .35rem;
}

/* Offset the second and 4th ring to the bottom */
.continent:nth-child(2),
.continent:nth-child(4){
    margin-top: calc(var(--header-offset) + 5.5 * var(--stroke));
    margin-left: calc(6.5 * var(--stroke));
    flex-direction: column-reverse;
}

.continent h2 {
    color: var(--color);
    font-weight: 400;
    font-size: 1.4rem;
}

.continent strong {
    font-weight: 600  ;
}

.continent ul {
    display: flex;
    justify-content: center;
    gap: 1rem;
}

.continent li {
    display: flex;
    align-items: center;
    gap: .5em;
    font-size: .7rem;
    font-weight: 600;
}

.continent li::before {
    width: 10px;
    height: 10px;
    content:'';
    display: block;
    border-radius: 100%;
    background: linear-gradient(to bottom, var(--medal-start), var(--medal-end));
    box-shadow: inset 0 -1px 2px var(--medal-shadow);
}

.gold {
    --medal-start: #fdf5c3;
    --medal-end: #fbe334;
    --medal-shadow: #dac215;
}

.silver {
    --medal-start: #f3f0f0;
    --medal-end: #d2cdca;
    --medal-shadow: #a4a09d;
}

.bronze {
    --medal-start: #fce7bd;
    --medal-end: #fa9e1b;
    --medal-shadow: #d6830d;
}

.ring {
    width: 100%;
    height: auto;
    aspect-ratio: 1;
    border-radius: 100%;
    position: relative;
}

.ring::before,
.ring::after {
    content: '';
    display: block;
    position: absolute;
    inset: 0;
    width: 100%;
    height: 100%;
    border-radius: 100%;
    color: var(--color);
    border: calc(2px + var(--stroke) * var(--ratio) * 1.5) solid var(--color);
    animation: border 1s;
}

.ring::after {
    border-color: transparent;
}

/* Chain overlap */
.continent:nth-child(1) .ring::after {
    border-right-color: var(--color);
    z-index: 6;
}

.continent:nth-child(2) .ring::after {
    border-top-color: var(--color);
    z-index: 5;
}

.continent:nth-child(3) .ring::before {
    border-top-color: var(--color);
    z-index: 4;
}

.continent:nth-child(4) .ring::before {
    z-index: 2;
}

.continent:nth-child(4) .ring::after {
    border-left-color: var(--color);
    z-index: 5;
}

.continent:nth-child(5) .ring::after {
    border-bottom-color: var(--color);
    z-index: 6;
}

/* Animation */
.card {
    overflow: hidden;
    animation: cardIn .8s both cubic-bezier(.56,1.57,.56,1);
}

.card::before {
    content:'';
    position: absolute;
    inset: 0;
    background: url(./images/paris-horizon.jpg) left bottom no-repeat ;
    animation: cardBg .7s 1s both ease-out ;
}

@keyframes cardIn {
    0% {
        opacity: 0;
        transform: scale(.7);
    }
}

@keyframes cardBg {
    0% {
        opacity: 0;
        transform: translateY(100px);
    }
}

@keyframes cardInMobile {
    0% {
        opacity: 0;
        transform: translateY(40px);
    }
}

.card > * {
    animation: cardContentIn 1s both cubic-bezier(.49,1.67,.26,.92);
    animation-delay: calc(.4s + .2s * var(--index, 0));
}

@keyframes cardContentIn {
    0% {
        transform: translateY(40px);
        opacity: 0;
    }
}

.ring::before,
.ring::after {
    animation:
            ringStroke .7s calc(.8s + .2s * var(--index)) cubic-bezier(.49,1.67,.26,.92) both,
            ringIn .7s  calc(.7s + .2s * var(--index)) cubic-bezier(.49,1.67,.26,.92) both;
}

@keyframes ringStroke {
    0% {
        border: var(--stroke) solid var(--color);
    }
}

@keyframes ringIn {
    0% {
        transform: scale(0) translateY(40px);

    }
}

/** Responsive **/
@media (max-width: 1200px) {
    .card {
        width: calc(100% - 2rem);
    }
}

@media (max-width: 950px) {
    :root {
        /* Why 38 ? graph width = (12 * stroke) * 3 + 2 */
        --stroke: calc((100vw - 6rem) / 38);
    }
}

@media (max-height: 700px) {
    :root {
        --stroke: 1rem;
    }
}

/* Screen is too narrow, we need a scrollbar */
@media (max-height: 600px) {
    body {
        overflow-y: scroll;
    }
    .card {
        padding: 1rem;
        margin-block: 1rem;
        height: auto;
    }
}

/* Mobile layout */
@media (max-width: 620px) {
    :root {
        --stroke: min(calc((100vw - 4rem) / 12), 1.2rem);
    }
    body {
        overflow-y: auto;
        overflow-x: hidden;
        background:
                linear-gradient(
                        rgba(0, 0, 0, .65),
                        rgba(0, 0, 0, .65)
                ),
                url(./images/poster-mobile.avif) center center / cover no-repeat,
                linear-gradient(135deg,#9bc8c5, #f6ead2,#a2deaa);
    }
    .card {
        gap: 3rem;
        padding: 0;
        margin-block: 1rem;
        padding-block: 2rem;
        max-height: none;
        height: auto;
        animation-name: cardInMobile;
    }
    h1, aside {
        padding-inline: 1rem;
    }
    h1 {
        font-size: 1.5rem;
        font-weight: bold;
    }
    .graph {
        overflow-y: hidden;
        overflow-x: scroll;
        scroll-snap-type: x proximity;
    }
    .continents {
        margin-inline: 1rem;
        margin-bottom: 1rem;
        width: calc(38 * var(--stroke));
    }
    .continent {
        scroll-snap-align: center;
    }
}

::-webkit-scrollbar {
    width: 7px;
    height: 7px;
}

::-webkit-scrollbar-track {
    background: transparent;
    padding: 1px;
}

::-webkit-scrollbar-thumb {
    background: #dadada;
    border-radius: 4px;
}