:root {
    font-family: "Segoe UI", Arial, sans-serif;
    color: #183746;
    background: #eef3f6;

    --pulse-a: #007f87;
    --pulse-b: #b75520;
    --result: #7042b5;
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
}

main {
    max-width: 1120px;
    margin: auto;
    padding: 32px 24px;
}

header {
    margin-bottom: 26px;
}

.eyebrow {
    font-size: 12px;
    font-weight: 750;
    letter-spacing: 1.5px;
    color: #426975;
}

h1 {
    font-size: clamp(30px, 4vw, 44px);
    letter-spacing: -1px;
    margin: 10px 0;
}

header p,
.section-heading p {
    color: #526b77;
    margin: 0;
    line-height: 1.5;
}

.settings {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 18px;
    margin-bottom: 20px;
}

.pulse-setting {
    padding: 20px;
    border-radius: 14px;
    background: white;
    border-top: 4px solid;
}

.pulse-a {
    border-color: var(--pulse-a);
}

.pulse-b {
    border-color: var(--pulse-b);
}

.pulse-setting h2 {
    font-size: 20px;
    margin: 0 0 18px;
}

.pulse-setting h2 span {
    display: block;
    margin-top: 5px;
    font-size: 13px;
    font-weight: 400;
    color: #526b77;
}

.pulse-setting label {
    display: block;
    margin: 15px 0 8px;
    font-size: 14px;
    font-weight: 600;
}

.pulse-setting output {
    float: right;
    font-variant-numeric: tabular-nums;
}

.pulse-setting select,
.pulse-setting input {
    width: 100%;
}

select,
button {
    font: inherit;
    color: #183746;
    background: white;
    border: 1px solid #b8cbd2;
    border-radius: 8px;
    padding: 10px 12px;
    cursor: pointer;
}

input[type="range"] {
    cursor: pointer;
    accent-color: var(--result);
}

.pulse-a input {
    accent-color: var(--pulse-a);
}

.pulse-b input {
    accent-color: var(--pulse-b);
}

.simulation {
    background: white;
    border: 1px solid #d4e0e6;
    border-radius: 18px;
    overflow: hidden;
}

.simulation-heading {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 16px;
    padding: 22px 24px 10px;
}

.simulation-heading h2 {
    font-size: 28px;
    margin: 6px 0;
    font-variant-numeric: tabular-nums;
}

.checkbox {
    font-size: 14px;
}

.checkbox input {
    accent-color: var(--result);
}

.legend {
    display: flex;
    flex-wrap: wrap;
    gap: 18px;
    padding: 8px 24px 14px;
    font-size: 13px;
    font-weight: 600;
}

.key-a {
    color: var(--pulse-a);
}

.key-b {
    color: var(--pulse-b);
}

.key-result {
    color: var(--result);
}

svg {
    display: block;
    width: 100%;
    height: auto;
}

.grid-note {
    font-size: 12px;
    text-align: center;
    color: #607781;
    padding: 0 18px;
    line-height: 1.6;
}

.controls {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 10px;
    padding: 16px 24px 8px;
}

.controls label {
    margin-left: auto;
    font-size: 14px;
}

.controls select {
    margin-left: 6px;
}

.primary {
    background: var(--result);
    border-color: var(--result);
    color: white;
    min-width: 100px;
}

button:hover {
    filter: brightness(0.95);
}

:focus-visible {
    outline: 3px solid #dfad36;
    outline-offset: 3px;
}

.timeline {
    display: flex;
    align-items: center;
    gap: 14px;
    padding: 14px 24px 22px;
    font-size: 14px;
}

.timeline input {
    flex: 1;
    min-width: 60px;
}

.timeline output {
    min-width: 58px;
    font-variant-numeric: tabular-nums;
}

.explanation {
    padding: 18px 24px;
    background: #f2edf9;
    color: #543484;
    line-height: 1.6;
}

.section-heading {
    margin: 30px 0 16px;
}

.section-heading h2 {
    margin: 0 0 8px;
    font-size: 23px;
}

.snapshots {
    display: grid;
    gap: 12px;
}

.snapshot {
    display: grid;
    grid-template-columns: 92px 1fr;
    align-items: center;
    padding: 8px 12px;
    text-align: left;
    background: white;
    border: 2px solid transparent;
    border-radius: 12px;
    width: 100%;
}

.snapshot.active {
    border-color: var(--result);
    background: #faf7ff;
}

.snapshot-label {
    font-weight: 700;
    padding-left: 8px;
}

.learning {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 18px;
    margin-top: 24px;
}

.learning article {
    padding: 24px;
    background: white;
    border-radius: 14px;
}

.learning h2 {
    font-size: 21px;
}

.learning p {
    line-height: 1.6;
    color: #526b77;
}

.learning .equation {
    font-size: 26px;
    color: var(--result);
}

.learning .question {
    background: #eee5fa;
}

.question .eyebrow {
    color: #71439b;
}

footer {
    padding: 22px 4px;
    font-size: 13px;
    color: #617985;
    line-height: 1.6;
}

@media (max-width: 650px) {
    main {
        padding: 22px 12px;
    }

    .settings,
    .learning {
        grid-template-columns: 1fr;
    }

    .simulation-heading {
        align-items: flex-start;
        flex-direction: column;
        padding: 18px;
    }

    .legend,
    .controls {
        padding-left: 18px;
        padding-right: 18px;
    }

    .controls label {
        margin-left: 0;
    }

    .snapshot {
        grid-template-columns: 65px 1fr;
        padding: 6px;
    }

    .snapshot-label {
        font-size: 12px;
        padding-left: 2px;
    }
}