:root {
    --bg1: #14070d;
    --bg2: #2a0d1a;
    --ink: #fff;
    --muted: rgba(255, 255, 255, .68);
    --glass: rgba(255, 255, 255, .07);
    --line: rgba(255, 255, 255, .16);
    --accent: #ff4d6d;
}

* { box-sizing: border-box; }

body {
    margin: 0;
    min-height: 100vh;
    padding: clamp(1.2rem, 5vw, 3rem) 1rem;
    display: flex;
    justify-content: center;
    font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
    color: var(--ink);
    background: radial-gradient(120% 80% at 50% 0%, var(--bg2), var(--bg1) 70%) fixed;
    touch-action: manipulation; /* stops double-tap zoom, so a quick second tap is not a second action */
}

.page { width: min(640px, 100%); }
.app { width: min(440px, 100%); margin: 0 auto; text-align: center; }

h1 { margin: 0; font-size: 1.7rem; letter-spacing: -.02em; }
.sub { margin: .4rem 0 0; color: var(--muted); }

.stage { margin: 1.6rem 0 1rem; }
.heart {
    width: 170px;
    height: auto;
    filter: drop-shadow(0 0 22px rgba(255, 77, 109, .45));
    will-change: transform;
}
body[data-playing="true"] .heart { filter: drop-shadow(0 0 34px rgba(255, 77, 109, .7)); }

.bpm { margin: .6rem 0 0; font-size: 2.6rem; font-weight: 300; line-height: 1; letter-spacing: -.03em; }
.bpm small { font-size: .9rem; font-weight: 600; letter-spacing: .12em; color: var(--muted); }

button, input { font: inherit; color: inherit; }
:focus-visible { outline: 2px solid #fff; outline-offset: 3px; }

.play {
    width: 88px; height: 88px;
    border-radius: 50%;
    border: 0;
    margin: .4rem auto 1.6rem;
    display: grid; place-items: center;
    cursor: pointer;
    color: #2a0d1a;
    background: #fff;
    box-shadow: 0 10px 30px rgba(255, 77, 109, .35);
    transition: transform .12s, box-shadow .2s;
}
.play:active { transform: scale(.94); }
.play svg { width: 38px; height: 38px; fill: currentColor; }
.play .i-pause { display: none; }
body[data-playing="true"] .play .i-play { display: none; }
body[data-playing="true"] .play .i-pause { display: block; }

.panel {
    margin-bottom: .9rem;
    padding: 1rem 1.1rem;
    border-radius: 18px;
    background: var(--glass);
    border: 1px solid var(--line);
    text-align: left;
}
.panel > label { display: block; margin-bottom: .6rem; font-size: .8rem; font-weight: 600; text-transform: uppercase; letter-spacing: .08em; color: var(--muted); }

input[type="range"] { width: 100%; accent-color: var(--accent); height: 28px; }

.chips { display: flex; flex-wrap: wrap; gap: .45rem; margin-top: .5rem; }
.panel > label + .chips { margin-top: 0; }
.chips button {
    padding: .4rem .8rem;
    border-radius: 999px;
    border: 1px solid var(--line);
    background: transparent;
    cursor: pointer;
    font-size: .9rem;
}
.chips button:hover { background: var(--glass); }
.chips button[aria-pressed="true"] { background: #fff; color: #2a0d1a; border-color: #fff; font-weight: 600; }

.timer-status { margin: .7rem 0 0; font-size: .92rem; color: var(--muted); }

.tip { margin: 1.2rem .4rem; font-size: .85rem; line-height: 1.5; color: var(--muted); }
footer { margin-top: 2rem; text-align: center; font-size: .82rem; }
footer a { color: var(--muted); }

/* the text under the player: what it is for, and common questions */
.info { margin-top: 3rem; padding-top: 2rem; border-top: 1px solid var(--line); }
.info h2 { margin: 0 0 1rem; font-size: 1.25rem; letter-spacing: -.01em; }
.info h2:not(:first-child) { margin-top: 2.2rem; }
.uses { margin: 0; padding: 0; list-style: none; display: grid; gap: .7rem; }
.uses li { padding: .9rem 1rem; border-radius: 14px; background: var(--glass); border: 1px solid var(--line); color: var(--muted); line-height: 1.5; }
.uses strong { display: block; color: var(--ink); margin-bottom: .15rem; }
.faq details { border-bottom: 1px solid var(--line); padding: .9rem 0; }
.faq summary { cursor: pointer; font-weight: 600; }
.faq p { margin: .6rem 0 0; color: var(--muted); line-height: 1.6; }

@media (prefers-reduced-motion: reduce) { .play { transition: none; } }

.keep { display: flex; align-items: center; gap: .5rem; margin-top: .8rem; color: var(--muted, #cbb); font-size: .92rem; min-height: 44px; cursor: pointer; }
.keep input { width: 20px; height: 20px; accent-color: var(--accent); }

/* back to the list of all apps */
.back { display: inline-flex; align-items: center; gap: .4rem; min-height: 44px; margin: 0 0 .5rem; padding: 0 1rem 0 .8rem; border: 1px solid var(--line, rgba(127,127,127,.4)); border-radius: 999px; color: var(--muted, var(--mut, inherit)); font-size: .92rem; font-weight: 600; text-decoration: none; background: transparent; }
.back:hover { color: var(--ink, inherit); border-color: currentColor; }
.back:focus-visible { outline: 3px solid var(--accent, var(--acc, #fff)); outline-offset: 2px; }
@media print { .back { display: none; } }

/* laptops and desktops: two columns instead of one phone-sized column */
@media (min-width: 900px) {
    .page { width: min(1000px, 100%); }
    .app { width: 100%; display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); column-gap: 3.5rem; align-items: center; }
    .app > header { grid-column: 1 / -1; grid-row: 1; margin-bottom: 1.5rem; }
    .app > .tip { grid-column: 1; grid-row: 4; }
    .app > .stage { grid-column: 1; grid-row: 2; margin: 1rem 0 .5rem; align-self: end; }
    .app > .play { grid-column: 1; grid-row: 3; margin: .4rem auto 0; align-self: start; }
    .app > .controls { grid-column: 2; grid-row: 2 / span 3; text-align: left; align-self: center; }
    .heart { width: 240px; }
    .info { width: min(720px, 100%); margin-left: auto; margin-right: auto; }
}