* {
    border: 0;
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

:root {
    --hue: 223;
    --bg: hsl(var(--hue), 10%, 90%);
    --fg: hsl(var(--hue), 10%, 10%);
    --primary: hsl(var(--hue), 90%, 45%);
    --primary-down: hsl(var(--hue), 90%, 65%);
    --trans-dur: 0.3s;
    font-size: calc(16px + (24 - 16) * (100vw - 320px) / (2560 - 320));
}

body {
    background-color: var(--bg);
    color: var(--fg);
    display: flex;
    font: 1em/1.5 Nunito, sans-serif;
    height: 100vh;
    transition:
        background-color var(--trans-dur),
        color var(--trans-dur);
}

main {
    display: grid;
    grid-gap: 3em 1.5em;
    margin: auto;
    max-width: 40em;
    padding: 3em 0;
    text-align: center;
    width: calc(100% - 3em);
}

h1 {
    font-size: 3em;
    line-height: 1;
    margin: 0 0 1.5rem;
}

p {
    margin: 0 0 1.5em;
}

.btn-link {
    background: var(--primary);
    border-radius: 1.5em;
    display: inline-block;
    outline: transparent;
    padding: 0.75em 1.5em;
    text-align: center;
    text-decoration: none;
    transition: background-color 0.15s linear;
}

.btn-link,
.btn-link:visited {
    color: hsl(0, 0%, 100%);
}

.btn-link:focus-visible,
.btn-link:hover {
    background: var(--primary-down);
}

.btn-link:hover {
    text-decoration: none;
}

.paper {
    display: block;
    margin: auto;
    overflow: visible;
    width: 100%;
    max-width: 224px;
    height: auto;
}

.paper__fill {
    fill: hsl(0, 0%, 100%);
}

.paper__outline,
.paper__lines {
    transition: stroke var(--trans-dur);
}

.paper__outline {
    stroke: hsl(var(--hue), 10%, 10%);
}

.paper__lines {
    stroke: hsl(var(--hue), 10%, 70%);
}

.paper__shadow {
    fill: hsl(var(--hue), 10%, 70%);
    transition: fill var(--trans-dur);
}

.paper__top,
.paper__bottom,
.paper__tear,
.paper__tear-fill {
    animation: paperTop 1.25s cubic-bezier(0.77, 0, 0.18, 1);
}

.paper__top,
.paper__bottom {
    transform-origin: 0 148px;
    transition: transform var(--trans-dur) cubic-bezier(0.77, 0, 0.18, 1);
}

.paper__top {
    transform: translate(0, 8px);
}

.paper__bottom {
    animation-name: paperBottom;
    transform: translate(0, 42px);
}

.paper__tear,
.paper__tear-fill {
    animation-timing-function: cubic-bezier(0.32, 0, 0.67, 0);
}

.paper__tear {
    animation-name: paperTear;
    stroke-dashoffset: 0;
}

.paper__tear-fill {
    animation-name: paperTearFill;
}

.paper__outline:hover .paper__top,
.paper__outline:hover .paper__bottom {
    transform: translate(0, 25px);
}

/* Dark theme */
@media (prefers-color-scheme: dark) {
    :root {
        --bg: hsl(var(--hue), 10%, 25%);
        --fg: hsl(var(--hue), 10%, 90%);
    }

    .paper__shadow:first-child {
        fill: hsl(var(--hue), 10%, 15%);
    }
}

/* Beyond mobile */
@media (min-width: 768px) {
    main {
        grid-template-columns: 1fr 2fr;
        align-items: center;
        text-align: left;
    }

    .paper {
        max-width: 300px;
    }
}

/* Animations */
@keyframes paperTop {

    from,
    40% {
        animation-timing-function: cubic-bezier(0.32, 0, 0.67, 0);
        transform: translate(0, 25px) rotate(0);
        transform-origin: 61px 148px;
    }

    70% {
        animation-timing-function: cubic-bezier(0.33, 1, 0.67, 1.5);
        transform: translate(0, 25px) rotate(-5deg);
        transform-origin: 61px 148px;
    }

    to {
        transform: translate(0, 8px) rotate(0);
        transform-origin: 0 148px;
    }
}

@keyframes paperBottom {

    from,
    40% {
        animation-timing-function: cubic-bezier(0.32, 0, 0.67, 0);
        transform: translate(0, 25px) rotate(0);
        transform-origin: 61px 148px;
    }

    70% {
        animation-timing-function: cubic-bezier(0.33, 1, 0.67, 1.5);
        transform: translate(0, 25px) rotate(5deg);
        transform-origin: 61px 148px;
    }

    to {
        transform: translate(0, 42px) rotate(0);
        transform-origin: 0 148px;
    }
}

@keyframes paperTear {

    from,
    40% {
        stroke-dashoffset: -198;
    }

    70%,
    to {
        stroke-dashoffset: 0;
    }
}

@keyframes paperTearFill {

    from,
    40% {
        width: 187px;
    }

    70%,
    to {
        width: 0;
    }
}