/* PID Control, Explained — one stylesheet, light and dark. Tokens match ferrolho.github.io. */

:root {
    --font-sans: 'Geist', ui-sans-serif, system-ui, -apple-system, sans-serif;
    --font-mono: 'Geist Mono', ui-monospace, 'SF Mono', Menlo, monospace;
    --font-serif: 'Instrument Serif', ui-serif, Georgia, serif; /* display words only */
    --font-math: 'STIX Two Text', 'Cambria Math', 'Times New Roman', serif;

    --bg: #f5f4ef;
    --bg-elev: #fbfaf7;
    --bg-sunk: #eceae3;
    --ink: #17160f;
    --ink-2: #4d4b44;
    --ink-3: #85827a;
    --line: #e1ded5;
    --line-2: #cfcbc0;
    --grid: rgba(23, 22, 15, 0.06);
    --accent: #ff4f00;
    --accent-ink: #c23c00;
    --accent-soft: rgba(255, 79, 0, 0.12);

    /* One colour per term, used everywhere the term appears. */
    --p: #2f6fed;
    --i: #17955a;
    --d: #8b5cf6;
    --warn: #e5484d;

    --radius: 12px;
    --shadow: 0 1px 0 rgba(23, 22, 15, 0.04), 0 14px 32px -22px rgba(23, 22, 15, 0.35);
    color-scheme: light;
}

@media (prefers-color-scheme: dark) {
    :root:not([data-theme='light']) {
        --bg: #0d0d0c;
        --bg-elev: #151513;
        --bg-sunk: #0a0a09;
        --ink: #edebe5;
        --ink-2: #b3b0a8;
        --ink-3: #7c7972;
        --line: #262522;
        --line-2: #363530;
        --grid: rgba(237, 235, 229, 0.06);
        --accent: #ff6a24;
        --accent-ink: #ff8a52;
        --accent-soft: rgba(255, 106, 36, 0.14);
        --p: #5b8ff9;
        --i: #3dbf7f;
        --d: #a78bfa;
        --warn: #ff6369;
        --shadow: 0 1px 0 rgba(0, 0, 0, 0.3), 0 14px 32px -22px rgba(0, 0, 0, 0.8);
        color-scheme: dark;
    }
}

:root[data-theme='dark'] {
    --bg: #0d0d0c;
    --bg-elev: #151513;
    --bg-sunk: #0a0a09;
    --ink: #edebe5;
    --ink-2: #b3b0a8;
    --ink-3: #7c7972;
    --line: #262522;
    --line-2: #363530;
    --grid: rgba(237, 235, 229, 0.06);
    --accent: #ff6a24;
    --accent-ink: #ff8a52;
    --accent-soft: rgba(255, 106, 36, 0.14);
    --p: #5b8ff9;
    --i: #3dbf7f;
    --d: #a78bfa;
    --warn: #ff6369;
    --shadow: 0 1px 0 rgba(0, 0, 0, 0.3), 0 14px 32px -22px rgba(0, 0, 0, 0.8);
    color-scheme: dark;
}

*,
*::before,
*::after {
    box-sizing: border-box;
}

html,
body {
    margin: 0;
    height: 100%;
}

body {
    background: var(--bg);
    color: var(--ink);
    font: 15px/1.5 var(--font-sans);
    -webkit-font-smoothing: antialiased;
}

button {
    font: inherit;
    color: inherit;
}

h1,
h2,
h3,
p {
    margin: 0;
}

sub {
    font-size: 0.7em;
}

/* ───────── Layout: one screen on desktop, stacked on small screens ───────── */

.app {
    display: grid;
    grid-template-rows: auto 1fr;
    height: 100vh;
    height: 100dvh;
}

.top {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 16px 24px;
    flex-wrap: wrap;
    padding: 12px 18px;
    border-bottom: 1px solid var(--line);
}

.title {
    display: flex;
    align-items: baseline;
    gap: 6px 22px;
    flex-wrap: wrap;
}

h1 {
    font-size: 19px;
    font-weight: 600;
    letter-spacing: -0.02em;
    white-space: nowrap;
}

h1 em {
    font-family: var(--font-serif);
    font-weight: 400;
    font-size: 1.15em;
    color: var(--accent);
}

.equation {
    font-family: var(--font-math);
    font-size: 19px;
    color: var(--ink-2);
    white-space: nowrap;
}

.var {
    font-style: italic;
}

.term {
    padding: 0 5px;
    border: 0;
    border-radius: 6px;
    background: transparent;
    font: inherit;
    cursor: pointer;
    transition: background 0.15s;
}

.term.p {
    color: var(--p);
}

.term.i {
    color: var(--i);
}

.term.d {
    color: var(--d);
}

.term:hover {
    background: var(--bg-sunk);
}

.actions {
    display: flex;
    flex-wrap: wrap;
    gap: 6px;
}

.btn {
    display: inline-flex;
    align-items: center;
    gap: 7px;
    height: 32px;
    padding: 0 12px;
    border: 1px solid var(--line-2);
    border-radius: 999px;
    background: var(--bg-elev);
    font-size: 13px;
    font-weight: 500;
    cursor: pointer;
    transition:
        border-color 0.15s,
        background 0.15s,
        color 0.15s;
}

.btn:hover {
    border-color: var(--ink-3);
}

.btn .ico {
    font-size: 11px;
    color: var(--ink-3);
}

.btn-learn {
    background: var(--ink);
    border-color: var(--ink);
    color: var(--bg);
}

.btn-learn:hover {
    background: var(--accent);
    border-color: var(--accent);
    color: #fff;
}

.main {
    display: grid;
    grid-template-columns: minmax(0, 1fr) 300px;
    min-height: 0;
}

.left {
    display: flex;
    flex-direction: column;
    gap: 10px;
    padding: 14px;
    min-height: 0;
}

.right {
    min-height: 0;
    border-left: 1px solid var(--line);
    background: var(--bg-elev);
    overflow-y: auto;
}

/* ───────── Cards ───────── */

.card {
    display: flex;
    flex-direction: column;
    min-height: 0;
    border: 1px solid var(--line);
    border-radius: var(--radius);
    background: var(--bg-elev);
    box-shadow: var(--shadow);
    overflow: hidden;
}

.card-head {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 12px;
    padding: 7px 12px;
    border-bottom: 1px solid var(--line);
    font-family: var(--font-mono);
    font-size: 11.5px;
    color: var(--ink-3);
}

.card-head .label {
    padding: 0;
    border: 0;
    background: none;
    font: inherit;
    letter-spacing: 0.04em;
    text-transform: uppercase;
    color: var(--ink-2);
}

button.label {
    cursor: pointer;
}

button.label:hover {
    color: var(--accent-ink);
}

canvas {
    display: block;
    width: 100%;
    flex: 1;
    min-height: 0;
}

.stage-card {
    flex: 0 0 auto;
}

#stage {
    height: clamp(130px, 22vh, 210px);
    flex: none;
    cursor: crosshair;
    background-image:
        linear-gradient(var(--grid) 1px, transparent 1px),
        linear-gradient(90deg, var(--grid) 1px, transparent 1px);
    background-size: 24px 24px;
    background-position: center;
}

.plot-card {
    flex: 1 1 0;
    min-height: 120px;
}

.legend {
    display: flex;
    flex-wrap: wrap;
    justify-content: flex-end;
    gap: 4px 14px;
}

.key {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    white-space: nowrap;
}

.key::before {
    content: '';
    width: 14px;
    height: 2px;
    border-radius: 2px;
    background: currentColor;
}

.key b {
    font-weight: 500;
    color: var(--ink);
    font-variant-numeric: tabular-nums;
    min-width: 4.5ch;
    text-align: right;
}

.key.target {
    color: var(--accent);
}

.key.target::before {
    background: repeating-linear-gradient(90deg, currentColor 0 4px, transparent 4px 7px);
}

.key.position,
.key.u {
    color: var(--ink);
}

.key.u::before {
    height: 3px;
}

.key.band::before {
    height: 8px;
    background: var(--accent-soft);
    border: 1px solid color-mix(in oklab, var(--accent) 30%, transparent);
}

.key.band,
.key.sat {
    color: var(--ink-3);
}

.key.sat::before {
    background: repeating-linear-gradient(90deg, var(--warn) 0 3px, transparent 3px 6px);
}

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

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

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

/* ───────── Metrics strip ───────── */

.metrics {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    border: 1px solid var(--line);
    border-radius: var(--radius);
    background: var(--bg-elev);
    overflow: hidden;
}

.metric {
    display: flex;
    flex-direction: column;
    align-items: flex-start;
    gap: 1px;
    padding: 7px 12px;
    border: 0;
    background: none;
    text-align: left;
    cursor: pointer;
    transition: background 0.15s;
}

.metric + .metric {
    border-left: 1px solid var(--line);
}

.metric:hover {
    background: var(--bg-sunk);
}

.metric .k {
    font-family: var(--font-mono);
    font-size: 11px;
    color: var(--ink-3);
}

.metric .v {
    font-size: 18px;
    font-weight: 600;
    letter-spacing: -0.02em;
    font-variant-numeric: tabular-nums;
}

.metric .v.pending {
    color: var(--ink-3);
    font-weight: 400;
}

/* ───────── Side panel ───────── */

.panel {
    padding: 14px 16px;
}

.panel + .panel {
    border-top: 1px solid var(--line);
}

.panel h2 {
    margin-bottom: 10px;
    font-family: var(--font-mono);
    font-size: 11.5px;
    font-weight: 500;
    letter-spacing: 0.06em;
    text-transform: uppercase;
    color: var(--ink-3);
}

.gain + .gain,
.field + .field {
    margin-top: 10px;
}

.gain label,
.field label {
    display: flex;
    align-items: baseline;
    gap: 8px;
    font-size: 13.5px;
}

.gain .name {
    padding: 0;
    border: 0;
    background: none;
    font-family: var(--font-math);
    font-size: 18px;
    cursor: pointer;
}

.gain.p .name {
    color: var(--p);
}

.gain.i .name {
    color: var(--i);
}

.gain.d .name {
    color: var(--d);
}

.gain .what {
    font-size: 12px;
    color: var(--ink-3);
}

output {
    margin-left: auto;
    font-family: var(--font-mono);
    font-size: 13px;
    font-variant-numeric: tabular-nums;
}

input[type='range'] {
    --c: var(--ink);
    width: 100%;
    height: 22px;
    margin: 2px 0 0;
    accent-color: var(--c);
    cursor: pointer;
}

.gain.p input {
    --c: var(--p);
}

.gain.i input {
    --c: var(--i);
}

.gain.d input {
    --c: var(--d);
}

#target {
    --c: var(--accent);
}

.presets {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 6px;
}

.preset {
    padding: 7px 10px;
    border: 1px solid var(--line-2);
    border-radius: 8px;
    background: var(--bg);
    font-size: 12.5px;
    font-weight: 500;
    text-align: left;
    line-height: 1.3;
    cursor: pointer;
    transition:
        border-color 0.15s,
        background 0.15s;
}

.preset:hover {
    border-color: var(--ink-3);
}

.preset[aria-pressed='true'] {
    border-color: var(--accent);
    background: var(--accent-soft);
    color: var(--accent-ink);
}

.preset-note {
    min-height: 3.2em;
    margin-top: 10px;
    font-size: 12.5px;
    color: var(--ink-2);
}

.switch {
    position: relative;
    display: flex;
    align-items: center;
    gap: 10px;
    margin-top: 12px;
    font-size: 13.5px;
    cursor: pointer;
}

.switch input {
    position: absolute;
    opacity: 0;
}

.switch > span {
    position: relative;
    flex: none;
    width: 30px;
    height: 18px;
    border-radius: 999px;
    background: var(--line-2);
    transition: background 0.15s;
}

.switch > span::after {
    content: '';
    position: absolute;
    top: 2px;
    left: 2px;
    width: 14px;
    height: 14px;
    border-radius: 50%;
    background: #fff;
    transition: transform 0.15s;
}

.switch input:checked + span {
    background: var(--ink);
}

.switch input:checked + span::after {
    transform: translateX(12px);
}

.switch input:focus-visible + span {
    outline: 2px solid var(--accent);
    outline-offset: 2px;
}

.link {
    padding: 0;
    border: 0;
    background: none;
    text-decoration: underline;
    text-decoration-color: var(--line-2);
    text-underline-offset: 3px;
    cursor: pointer;
}

.link:hover {
    text-decoration-color: var(--accent);
}

:focus-visible {
    outline: 2px solid var(--accent);
    outline-offset: 2px;
}

/* ───────── Learn drawer ───────── */

.drawer[hidden] {
    display: none;
}

.drawer {
    position: fixed;
    inset: 0;
    z-index: 10;
}

.drawer-backdrop {
    position: absolute;
    inset: 0;
    background: rgba(0, 0, 0, 0.25);
    animation: fade 0.2s;
}

.drawer-panel {
    position: absolute;
    top: 0;
    right: 0;
    bottom: 0;
    display: flex;
    flex-direction: column;
    width: min(440px, 100vw);
    background: var(--bg);
    border-left: 1px solid var(--line);
    box-shadow: -20px 0 40px -20px rgba(0, 0, 0, 0.3);
    animation: slide 0.22s cubic-bezier(0.2, 0.8, 0.2, 1);
}

@keyframes fade {
    from {
        opacity: 0;
    }
}

@keyframes slide {
    from {
        transform: translateX(30px);
        opacity: 0;
    }
}

.drawer-head {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 14px 18px;
    border-bottom: 1px solid var(--line);
}

.drawer-head h2 {
    font-size: 17px;
}

.icon-btn {
    width: 30px;
    height: 30px;
    border: 0;
    border-radius: 50%;
    background: none;
    color: var(--ink-3);
    cursor: pointer;
}

.icon-btn:hover {
    background: var(--bg-sunk);
    color: var(--ink);
}

.tabs {
    display: flex;
    gap: 4px;
    padding: 10px 18px;
    border-bottom: 1px solid var(--line);
}

.tabs button {
    padding: 5px 12px;
    border: 1px solid transparent;
    border-radius: 999px;
    background: none;
    font-size: 13px;
    color: var(--ink-2);
    cursor: pointer;
}

.tabs button[aria-selected='true'] {
    border-color: var(--line-2);
    background: var(--bg-elev);
    color: var(--ink);
}

.drawer-body {
    flex: 1;
    overflow-y: auto;
    padding: 16px 18px 28px;
}

.topic {
    display: block;
    width: 100%;
    padding: 12px 14px;
    border: 1px solid var(--line);
    border-left: 3px solid var(--line-2);
    border-radius: 8px;
    background: var(--bg-elev);
    text-align: left;
    cursor: pointer;
}

.topic + .topic {
    margin-top: 8px;
}

.topic:hover {
    border-color: var(--ink-3);
}

.topic.p {
    border-left-color: var(--p);
}

.topic.i {
    border-left-color: var(--i);
}

.topic.d {
    border-left-color: var(--d);
}

.topic strong {
    display: block;
    font-size: 14.5px;
}

.topic span {
    font-size: 13px;
    color: var(--ink-3);
}

.back {
    margin-bottom: 14px;
    padding: 0;
    border: 0;
    background: none;
    font-size: 13px;
    color: var(--ink-3);
    cursor: pointer;
}

.back:hover {
    color: var(--accent-ink);
}

.article {
    font-size: 14.5px;
    line-height: 1.65;
    color: var(--ink-2);
}

.article h2 {
    font-size: 22px;
    letter-spacing: -0.02em;
    color: var(--ink);
    margin-bottom: 12px;
}

.article h3 {
    margin: 20px 0 6px;
    font-size: 15px;
    color: var(--ink);
}

.article p + p,
.article p + ul,
.article ul + p {
    margin-top: 10px;
}

.article ul,
.article ol {
    padding-left: 1.2em;
    margin: 8px 0 0;
}

.article li + li {
    margin-top: 4px;
}

.article strong {
    color: var(--ink);
}

.article .formula {
    margin: 12px 0;
    padding: 10px 14px;
    border: 1px solid var(--line);
    border-radius: 8px;
    background: var(--bg-elev);
    font-family: var(--font-math);
    font-size: 18px;
    color: var(--ink);
    text-align: center;
}

.related {
    margin-top: 24px;
    padding-top: 14px;
    border-top: 1px solid var(--line);
    font-size: 13px;
}

.related h4 {
    margin: 0 0 8px;
    font-family: var(--font-mono);
    font-size: 11px;
    font-weight: 500;
    letter-spacing: 0.06em;
    text-transform: uppercase;
    color: var(--ink-3);
}

.related button {
    margin: 0 6px 6px 0;
    padding: 4px 10px;
    border: 1px solid var(--line-2);
    border-radius: 999px;
    background: none;
    font-size: 12.5px;
    cursor: pointer;
}

.related button:hover {
    border-color: var(--accent);
    color: var(--accent-ink);
}

/* ───────── Small screens: stack and let the page scroll ───────── */

@media (max-width: 900px) {
    .app {
        height: auto;
    }
    .main {
        grid-template-columns: 1fr;
    }
    .right {
        border-left: 0;
        border-top: 1px solid var(--line);
        overflow: visible;
    }
    .plot-card {
        flex: none;
        height: 220px;
    }
    .card-head .hint {
        display: none;
    }
}

@media (max-width: 560px) {
    .metrics {
        grid-template-columns: 1fr 1fr;
    }
    .metric:nth-child(3) {
        border-left: 0;
    }
    .metric:nth-child(n + 3) {
        border-top: 1px solid var(--line);
    }
    .equation {
        font-size: 17px;
    }
}

@media (prefers-reduced-motion: reduce) {
    .drawer-panel,
    .drawer-backdrop {
        animation: none;
    }
}