/* ============================================================
   EyeTech — Precision Scientific Instrument
   Identity: amber phosphor readout · tactile keys · one accent.
   Built for a mixed audience (low-vision + screen-reader):
   distinctive AND every contrast pair verified WCAG AA/AAA.
   ============================================================ */

:root {
    --zoom: 1;
    --font-ui: "Space Grotesk", "Segoe UI", system-ui, sans-serif;
    --font-readout: "JetBrains Mono", ui-monospace, "Consolas", monospace;
    --letter-spacing: normal;
    --line-height: 1.3;

    /* Shape & rhythm */
    --r-key: 12px;
    --r-panel: 14px;
    --r-sm: 8px;
    --r-pill: 999px;
    --s1: 6px; --s2: 10px; --s3: 16px; --s4: 24px; --s5: 34px;

    /* Motion */
    --ease: cubic-bezier(0.22, 1, 0.36, 1);
    --ease-soft: cubic-bezier(0.33, 1, 0.68, 1);
    --dur: 0.16s; --dur-slow: 0.32s;

    /* z-index scale */
    --z-grain: 0; --z-sticky: 50; --z-focus: 60; --z-backdrop: 90; --z-modal: 100;
}

/* =============================== THEMES =============================== */

/* 1. Instrument — signature default. Amber readout on cool charcoal. */
[data-theme="slate"] {
    --bg: #0b0d11;
    --bg-2: #0e1116;
    --panel: #12151b;
    --readout-bg: #0a0c10;
    --key: #1b1f27;
    --key-top: #242a35;          /* gradient highlight for tactility */
    --key-edge: #05060a;         /* bottom shadow lip */
    --key-hi: #283040;
    --text: #f4f6fa;
    --text-dim: #aab5c4;
    --accent: #ffb000;           /* the one accent */
    --accent-2: #ffc24d;
    --accent-soft: rgba(255, 176, 0, 0.14);
    --accent-ink: #1a1200;
    --readout: #ffb524;
    --readout-glow: rgba(255, 176, 0, 0.22);
    --op: #ffc24d;
    --sci: #aab5c4;
    --danger: #ff7a7a;
    --border: #29313d;
    --hair: #1e242e;
    --ring: #ffb000;
    --grain: 0.035;
    --key-bd: 1px;
}

/* 2. High Contrast — pure black / yellow. Flat, thick borders, no gradient. */
[data-theme="high-contrast"] {
    --bg: #000; --bg-2: #000; --panel: #000; --readout-bg: #000;
    --key: #000; --key-top: #000; --key-edge: #000; --key-hi: #1c1c1c;
    --text: #ffff00; --text-dim: #ffff00;
    --accent: #ffff00; --accent-2: #ffff00; --accent-soft: rgba(255,255,0,0.16); --accent-ink: #000;
    --readout: #ffff00; --readout-glow: transparent;
    --op: #00ffff; --sci: #00ffff; --danger: #ff5b5b;
    --border: #ffff00; --hair: #ffff00; --ring: #00ffff;
    --grain: 0; --key-bd: 2.5px;
}

/* 3. Ocean — calm teal, amber accent retained for identity continuity */
[data-theme="ocean"] {
    --bg: #04222a; --bg-2: #052831; --panel: #073642; --readout-bg: #04232a;
    --key: #0b4651; --key-top: #0f5663; --key-edge: #021519; --key-hi: #0f5f6f;
    --text: #eaf6f4; --text-dim: #a7cccc;
    --accent: #ffc857; --accent-2: #ffd87f; --accent-soft: rgba(255,200,87,0.16); --accent-ink: #04232a;
    --readout: #ffd166; --readout-glow: rgba(255,200,87,0.20);
    --op: #ffd87f; --sci: #a7cccc; --danger: #ff9a90;
    --border: #1d5d69; --hair: #134a55; --ring: #ffc857;
    --grain: 0.03; --key-bd: 1px;
}

/* 4. Light — ink on warm white, amber as action accent */
[data-theme="light"] {
    --bg: #eceef2; --bg-2: #f4f6f9; --panel: #ffffff; --readout-bg: #ffffff;
    --key: #ffffff; --key-top: #ffffff; --key-edge: #d4d9e1; --key-hi: #eef1f6;
    --text: #0b1016; --text-dim: #46505f;
    --accent: #b86b00; --accent-2: #8a5000; --accent-soft: rgba(184,107,0,0.12); --accent-ink: #ffffff;
    --readout: #1a1f27; --readout-glow: transparent;
    --op: #b86b00; --sci: #46505f; --danger: #c62828;
    --border: #c6cdd8; --hair: #dde2ea; --ring: #b86b00;
    --grain: 0; --key-bd: 1.5px;
}

/* =============================== FONT MODES =============================== */
[data-font="standard"] {
    --font-ui: "Space Grotesk", "Segoe UI", system-ui, sans-serif;
    --font-readout: "JetBrains Mono", ui-monospace, "Consolas", monospace;
    --letter-spacing: normal; --line-height: 1.3;
}
[data-font="mono"] {
    --font-ui: "JetBrains Mono", ui-monospace, "Consolas", monospace;
    --font-readout: "JetBrains Mono", ui-monospace, "Consolas", monospace;
    --letter-spacing: -0.2px; --line-height: 1.4;
}
[data-font="dyslexic"] {
    --font-ui: "Comic Sans MS", "Chalkboard SE", Verdana, sans-serif;
    --font-readout: "Comic Sans MS", "Chalkboard SE", Verdana, sans-serif;
    --letter-spacing: 0.03em; --line-height: 1.55;
}

/* =============================== RESET =============================== */
* { box-sizing: border-box; }

html {
    -webkit-text-size-adjust: 100%;
    font-size: calc(16px * var(--zoom));   /* zoom scales the whole UI */
    scroll-padding-block: var(--s3) 88px;
}

body {
    margin: 0;
    background: var(--bg);
    color: var(--text);
    font-family: var(--font-ui);
    letter-spacing: var(--letter-spacing);
    line-height: var(--line-height);
    font-size: 1.0625rem;
    min-height: 100dvh;
    overflow-x: hidden;
    overflow-y: auto;
    transition: background-color var(--dur-slow) var(--ease), color var(--dur-slow) var(--ease);
}

/* Solid tonal layers keep the instrument calm and legible. */

/* =============================== SKIP LINK =============================== */
.skip-link {
    position: absolute; top: 0; left: 12px;
    background: var(--accent); color: var(--accent-ink);
    padding: 12px 18px; z-index: var(--z-modal);
    border-radius: var(--r-sm); font-weight: 700; text-decoration: none;
    max-width: calc(100% - 24px);
    transform: translateY(calc(-100% - 12px));
    transition: transform var(--dur) var(--ease);
}
.skip-link:focus { transform: translateY(12px); }

/* Screen-reader-only utility (visually hidden, still announced) */
.sr-only {
    position: absolute !important;
    width: 1px; height: 1px;
    padding: 0; margin: -1px;
    overflow: hidden; clip: rect(0, 0, 0, 0);
    white-space: nowrap; border: 0;
}

/* Disabled buttons (e.g. hex digits A–F outside HEX mode) read as unavailable */
button:disabled, button[aria-disabled="true"] {
    opacity: 0.32;
    cursor: not-allowed;
    filter: grayscale(0.4);
}

/* =============================== FOCUS =============================== */
button, input, select { font-family: inherit; border: none; cursor: pointer; outline: none; letter-spacing: inherit; }

button:focus-visible, input:focus-visible, select:focus-visible, a:focus-visible, summary:focus-visible,
input:focus, select:focus {
    outline: 3px solid var(--ring);
    outline-offset: 2px;
    border-radius: var(--r-sm);
    position: relative;
    z-index: var(--z-focus);
}

button:focus-visible, input:focus-visible, select:focus-visible, a:focus-visible,
summary:focus-visible {
    scroll-margin-block: var(--s3) 96px;
}

/* =============================== LAYOUT =============================== */
/* Narrow: single fluid column that fills the width.
   Wide: two-pane — console (display + history) left, keypad right.
   Fills the screen at every resolution. */
.container {
    width: 100%; max-width: 100%; margin: 0 auto;
    padding:
        max(var(--s2), env(safe-area-inset-top))
        max(var(--s3), env(safe-area-inset-right))
        max(var(--s3), env(safe-area-inset-bottom))
        max(var(--s3), env(safe-area-inset-left));
    min-height: 100dvh; display: flex; flex-direction: column; gap: var(--s2);
    position: relative; z-index: 1;
}
.console { display: flex; flex-direction: column; gap: var(--s2); min-width: 0; }

@media (min-width: 920px) {
    .container {
        display: grid;
        grid-template-columns: minmax(320px, 0.85fr) minmax(440px, 1.15fr);
        grid-template-rows: auto auto auto;
        grid-template-areas:
            "head head"
            "console tabs"
            "console pad";
        column-gap: clamp(var(--s4), 3vw, 48px);
        row-gap: var(--s3);
        max-width: 1600px;
        padding: var(--s3) var(--s4) var(--s4);
        align-items: start;
        align-content: start;
    }
    .hud-bar { grid-area: head; }
    .console { grid-area: console; position: sticky; top: var(--s3); }
    .tab-bar { grid-area: tabs; }
    .tab-content { grid-area: pad; min-height: 0; }
    .history { max-height: min(42vh, 420px); }
    .display-container { min-height: 190px; }
}
@media (min-width: 1180px) {
    .container { column-gap: 48px; }
    .display-container { min-height: 210px; }
    .btn { min-height: 68px; }
}

/* =============================== HEADER =============================== */
.hud-bar {
    display: flex; justify-content: space-between; align-items: center;
    gap: var(--s2); flex-shrink: 0;
}
.app-title {
    font-size: 1rem; font-weight: 700; letter-spacing: -0.01em;
    margin: 0 auto 0 0; color: var(--text);
    display: flex; align-items: center; gap: 8px;
    min-width: 0;
}
.app-title .mark { color: var(--accent); font-size: 1.2rem; }
.app-tag {
    font-size: 0.65rem; font-weight: 700; letter-spacing: 0.06em;
    color: var(--accent); background: var(--accent-soft);
    border: 1px solid var(--accent); border-radius: var(--r-pill);
    padding: 3px 9px; text-transform: uppercase;
}
.hud-right { display: flex; gap: var(--s1); align-items: center; flex-shrink: 0; }

.hud-btn {
    background: var(--panel); border: 1.5px solid var(--border); color: var(--text);
    padding: 8px 12px; font-weight: 600; border-radius: var(--r-sm);
    font-size: 0.875rem; min-height: 44px; display: inline-flex; align-items: center; justify-content: center; gap: 6px;
    transition: transform var(--dur) var(--ease), background-color var(--dur) var(--ease),
                color var(--dur) var(--ease), border-color var(--dur) var(--ease);
}
.hud-btn:hover { border-color: var(--accent); }
.hud-btn:active { transform: scale(0.94); }
.hud-btn.active { background: var(--accent); color: var(--accent-ink); border-color: var(--accent); }

/* =============================== MODE TABS =============================== */
.tab-bar {
    display: flex; gap: var(--s1); flex-shrink: 0;
    overflow-x: auto; overscroll-behavior-inline: contain;
    scrollbar-width: thin; scroll-snap-type: inline proximity;
    padding: 2px 2px var(--s1);
}
.tab-btn {
    flex: 0 0 auto; min-width: 88px; scroll-snap-align: start;
    background: var(--panel); color: var(--text-dim);
    border: 1.5px solid var(--hair); padding: 10px 12px; border-radius: var(--r-sm);
    font-weight: 600; font-size: 0.82rem; letter-spacing: 0.01em;
    min-height: 46px;
    transition: transform var(--dur) var(--ease), background-color var(--dur) var(--ease),
                color var(--dur) var(--ease), border-color var(--dur) var(--ease);
}
.tab-btn:hover { color: var(--text); border-color: var(--accent); }
.tab-btn.active {
    background: var(--accent-soft); color: var(--accent); border-color: var(--accent);
}

/* =============================== DISPLAY (HERO READOUT) =============================== */
.display-container {
    background: var(--readout-bg);
    border: 1.5px solid var(--border);
    border-radius: var(--r-panel);
    padding: var(--s3);
    text-align: right;
    min-height: 132px;
    display: flex; flex-direction: column; justify-content: space-between;
    flex-shrink: 0;
    box-shadow: inset 0 1px 0 rgba(255,255,255,0.04);
    overflow: hidden;
    position: relative;
}
#status-bar {
    display: flex; flex-wrap: wrap; justify-content: space-between; align-items: center; gap: var(--s1);
    font-family: var(--font-readout);
    font-size: 0.72rem; letter-spacing: 0.12em; font-weight: 700; text-transform: uppercase;
}
#status-bar .status-badge {
    border: 1px solid var(--hair); color: var(--text-dim);
    border-radius: var(--r-pill); padding: 3px 11px;
}
.read-btn {
    font-family: var(--font-ui); font-size: 0.74rem; font-weight: 700; letter-spacing: 0.04em;
    text-transform: none; color: var(--text-dim);
    background: transparent; border: 1px solid var(--hair); border-radius: var(--r-pill);
    padding: 4px 12px; min-height: 32px; margin-right: auto;
    transition: color var(--dur) var(--ease), border-color var(--dur) var(--ease);
}
.read-btn:hover { color: var(--accent); border-color: var(--accent); }
.read-btn:active { transform: scale(0.95); }

.display-tool {
    min-height: 36px; padding: 6px 10px;
    background: transparent; color: var(--text-dim);
    border: 1px solid var(--hair); border-radius: var(--r-sm);
    font-size: 0.75rem; font-weight: 700; line-height: 1.1;
    transition: color var(--dur) var(--ease), border-color var(--dur) var(--ease), background-color var(--dur) var(--ease);
}
.display-tool:hover:not(:disabled) { color: var(--text); border-color: var(--accent); }
.display-tool.active, .display-tool[aria-pressed="true"] {
    color: var(--accent); border-color: var(--accent); background: var(--accent-soft);
}
.expression-label {
    margin: var(--s2) 0 4px; color: var(--text-dim);
    font-size: 0.75rem; font-weight: 700; text-align: left;
}
.expression-input {
    width: 100%; min-height: 44px; padding: 8px 10px;
    background: var(--panel); color: var(--text);
    border: 1.5px solid var(--hair); border-radius: var(--r-sm);
    font-family: var(--font-readout); font-size: 1.15rem; text-align: right;
    caret-color: var(--accent); cursor: text;
}
.expression-input::placeholder { color: var(--text-dim); opacity: 1; }
.expression-input:hover { border-color: var(--border); }

.result-note {
    min-height: 1.2em; margin-top: 4px; color: var(--text-dim);
    font-size: 0.75rem; font-weight: 600; text-align: right;
}
.result-options { margin-top: var(--s1); border-top: 1px solid var(--hair); }
.result-options > summary {
    min-height: 36px; display: flex; align-items: center; justify-content: flex-end; gap: 8px;
    color: var(--text-dim); cursor: pointer; list-style: none;
    font-size: 0.75rem; font-weight: 700;
}
.result-options > summary::-webkit-details-marker { display: none; }
.result-options > summary::after { content: "+"; color: var(--accent); font-size: 1rem; }
.result-options[open] > summary::after { content: "−"; }
.result-options-body { display: grid; gap: var(--s2); padding: 2px 0 var(--s1); }
.format-controls, .copy-controls { display: flex; flex-wrap: wrap; justify-content: flex-end; gap: var(--s1); }

/* =============================== HISTORY =============================== */
.history {
    display: flex; flex-direction: column;
    background: var(--panel); border: 1.5px solid var(--hair);
    border-radius: var(--r-panel); overflow: hidden;
}
.history-head {
    display: flex; justify-content: space-between; align-items: center;
    padding: 12px var(--s3);
    font-size: 0.875rem; font-weight: 700; letter-spacing: 0.01em;
    color: var(--text-dim); flex-shrink: 0;
    min-height: 48px; cursor: pointer; list-style: none;
}
.history-head::-webkit-details-marker { display: none; }
.history-head::after { content: "+"; color: var(--accent); font-size: 1.25rem; line-height: 1; }
.history[open] .history-head { border-bottom: 1.5px solid var(--hair); }
.history[open] .history-head::after { content: "−"; }
.history-count { margin-left: auto; margin-right: var(--s2); font-weight: 600; color: var(--text-dim); }
.history-actions { display: flex; justify-content: flex-end; padding: var(--s2) var(--s2) 0; }
.history-clear {
    font-family: var(--font-ui); font-size: 0.8rem; font-weight: 700; letter-spacing: 0.01em;
    background: transparent; color: var(--text-dim); border: 1px solid var(--hair);
    border-radius: var(--r-sm); padding: 7px 10px; min-height: 40px;
    transition: color var(--dur) var(--ease), border-color var(--dur) var(--ease);
}
.history-clear:hover { color: var(--danger); border-color: var(--danger); }
.history-list {
    list-style: none; margin: 0; padding: var(--s1); overflow-y: auto; min-height: 0;
    scrollbar-width: thin;
}
.history-empty { color: var(--text-dim); font-size: 0.92rem; padding: var(--s3); line-height: 1.5; }
.history-item {
    width: 100%; display: flex; flex-direction: column; align-items: flex-end; gap: 2px;
    background: transparent; border: none; border-radius: var(--r-sm);
    padding: 10px var(--s3); text-align: right;
    transition: background-color var(--dur) var(--ease);
}
.history-list li + li { border-top: 1px solid var(--hair); }
.history-item:hover { background: var(--key-hi); }
.history-item .h-expr { font-family: var(--font-readout); font-size: 0.95rem; color: var(--text-dim); word-break: break-all; }
.history-item .h-res { font-family: var(--font-readout); font-size: 1.25rem; font-weight: 800; color: var(--readout); word-break: break-all; }

#visual-display {
    color: var(--text-dim); font-family: var(--font-readout);
    font-size: 1.05rem; min-height: 1.4rem; margin-top: 4px;
    word-break: break-all; letter-spacing: 0.01em;
}
#result-display {
    display: block;
    color: var(--readout); font-family: var(--font-readout);
    font-size: 2.5rem; font-weight: 800; line-height: 1.05;
    word-break: break-all; letter-spacing: -0.01em;
    text-shadow: 0 0 22px var(--readout-glow);
    transition: color var(--dur) var(--ease);
}
#result-display.flash { animation: settle var(--dur-slow) var(--ease); }
#result-display.error { color: var(--danger); font-size: clamp(1.8rem, 8vw, 2.6rem); text-shadow: none; }

/* =============================== KEYPAD =============================== */
.tab-content { display: none; padding: 2px 1px var(--s3); min-width: 0; }
.tab-content.active { display: block; }
.tab-content[hidden] { display: none !important; }

.keypad-grid { display: grid; grid-template-columns: repeat(5, 1fr); gap: var(--s2); }
.col-4 { grid-template-columns: repeat(4, 1fr); }
.col-3 { grid-template-columns: repeat(3, 1fr); }
.col-2 { grid-template-columns: repeat(2, 1fr); }

/* Tactile key: gradient face, highlight lip, shadow edge that collapses on press */
.btn {
    background: linear-gradient(180deg, var(--key-top), var(--key));
    border: var(--key-bd) solid var(--border);
    color: var(--text);
    font-size: 1.5rem; font-weight: 600;
    border-radius: var(--r-key);
    min-height: 56px;
    display: flex; align-items: center; justify-content: center; line-height: 1.1; text-align: center;
    box-shadow: inset 0 1px 0 rgba(255,255,255,0.06), 0 3px 0 var(--key-edge);
    transition: transform var(--dur) var(--ease), background-color var(--dur) var(--ease),
                border-color var(--dur) var(--ease), box-shadow var(--dur) var(--ease), filter var(--dur) var(--ease);
    -webkit-tap-highlight-color: transparent;
}
@media (hover: hover) {
    .btn:hover { border-color: var(--accent); filter: brightness(1.08); }
}
.btn:active {
    transform: translateY(3px);
    box-shadow: inset 0 1px 0 rgba(255,255,255,0.05), 0 0 0 var(--key-edge);
    filter: brightness(1.12);
}

/* Zoning by treatment, not by extra hues */
.btn.digit { font-size: 1.9rem; font-weight: 700; }
.btn.op    { color: var(--op); font-weight: 700; font-size: 1.85rem; }
.btn.sci   { color: var(--sci); font-size: 1.25rem; font-weight: 600; }
.btn.const { color: var(--op); font-size: 1.5rem; }
.btn.func  { color: var(--text-dim); font-size: 1.15rem; font-weight: 600; }
.btn.danger{ color: var(--danger); }
.btn.equals {
    background: linear-gradient(180deg, var(--accent-2), var(--accent));
    color: var(--accent-ink); border-color: var(--accent);
    font-size: 2.2rem; font-weight: 800;
    box-shadow: inset 0 1px 0 rgba(255,255,255,0.25), 0 3px 0 color-mix(in srgb, var(--accent) 55%, black);
}
.btn.equals:active { box-shadow: inset 0 1px 0 rgba(255,255,255,0.2), 0 0 0 var(--key-edge); }

.span-2 { grid-column: span 2; }

.full-width {
    width: 100%; margin-top: var(--s3); padding: 18px; font-size: 1.3rem;
    background: linear-gradient(180deg, var(--accent-2), var(--accent));
    color: var(--accent-ink); font-weight: 800; border-radius: var(--r-key);
    border: 1.5px solid var(--accent); min-height: 60px;
    box-shadow: inset 0 1px 0 rgba(255,255,255,0.25), 0 3px 0 color-mix(in srgb, var(--accent) 55%, black);
    transition: transform var(--dur) var(--ease), filter var(--dur) var(--ease);
}
.full-width:hover { filter: brightness(1.06); }
.full-width:active { transform: translateY(2px); }

/* =============================== TOOL UIs =============================== */
.tool-ui { padding: 2px; }
.section-title {
    color: var(--text); margin: var(--s2) 0; font-size: 1.1rem; font-weight: 700;
    letter-spacing: 0.02em; border-bottom: 1.5px solid var(--hair); padding-bottom: 8px;
}
.tool-header { display: flex; gap: var(--s2); margin-bottom: var(--s3); }
.tool-btn {
    flex: 1; padding: 14px; background: var(--panel); color: var(--text);
    border: 1.5px solid var(--border); border-radius: var(--r-sm);
    font-weight: 700; font-size: 1rem; min-height: 52px; letter-spacing: 0.02em;
    transition: transform var(--dur) var(--ease), background-color var(--dur) var(--ease),
                color var(--dur) var(--ease), border-color var(--dur) var(--ease);
}
.tool-btn:hover { border-color: var(--accent); }
.tool-btn:active { transform: scale(0.97); }
.tool-btn.active { background: var(--accent-soft); color: var(--accent); border-color: var(--accent); }

label { display: block; font-weight: 700; margin-bottom: 8px; font-size: 1rem; }
label small { font-weight: 500; color: var(--text-dim); }

.big-input, .big-select, .half-input {
    width: 100%; padding: 16px; font-size: 1.2rem; font-weight: 600;
    font-family: var(--font-readout);
    background: var(--panel); color: var(--text);
    border: 1.5px solid var(--border); margin-bottom: var(--s3); border-radius: var(--r-sm);
    transition: border-color var(--dur) var(--ease);
}
.big-select { font-family: var(--font-ui); }
.big-input::placeholder, .half-input::placeholder { color: var(--text-dim); font-weight: 500; }
.big-input:hover, .big-select:hover, .half-input:hover { border-color: var(--accent); }

.row { display: flex; gap: var(--s3); align-items: flex-start; margin-bottom: var(--s3); }
.half-box { flex: 1; display: flex; flex-direction: column; }

/* =============================== MATRIX =============================== */
.matrix-grid { display: grid; gap: var(--s2); margin-bottom: var(--s3); justify-content: center; }
.matrix-grid input {
    width: 64px; height: 64px; text-align: center; font-family: var(--font-readout);
    background: var(--panel); color: var(--text);
    border: 1.5px solid var(--border); font-size: 1.3rem; font-weight: 700;
    border-radius: var(--r-sm); transition: border-color var(--dur) var(--ease);
}
.matrix-grid input:hover, .matrix-grid input:focus { border-color: var(--accent); }

/* =============================== GRAPH =============================== */
.graph-stage {
    width: 100%; background: var(--readout-bg); border: 1.5px solid var(--border);
    border-radius: var(--r-panel); padding: 10px; margin-bottom: var(--s3);
    box-shadow: inset 0 0 50px rgba(0,0,0,0.3);
}
#graph-canvas { width: 100%; aspect-ratio: 5 / 3; display: block; border-radius: var(--r-sm); }
.graph-desc {
    font-size: 1.02rem; font-weight: 500; line-height: 1.55;
    background: var(--panel); border: 1.5px solid var(--hair);
    border-radius: var(--r-sm); padding: 16px; margin: 0 0 var(--s3);
}
.graph-desc strong { color: var(--accent); font-weight: 700; }

/* =============================== GCSE SOLVERS =============================== */
.gcse-card {
    background: var(--panel);
    border: 1.5px solid var(--hair);
    border-radius: var(--r-panel);
    padding: var(--s3);
    margin-bottom: var(--s3);
}
.gcse-card .section-title { margin-top: 0; }
.gcse-card .full-width { margin-top: var(--s1); }
.gcse-card .row { margin-bottom: var(--s2); }
.card-note { color: var(--text-dim); font-size: 0.92rem; line-height: 1.5; margin: 0 0 var(--s2); }

/* About panel in settings */
.about p { margin: 6px 0; line-height: 1.5; font-size: 1rem; color: var(--text); }
.about a { color: var(--accent); font-weight: 700; }
.solver-out {
    font-size: 1.05rem; font-weight: 600; line-height: 1.55;
    background: var(--readout-bg); border: 1.5px solid var(--hair);
    border-radius: var(--r-sm); padding: 14px; margin: var(--s2) 0 0; color: var(--text);
}

/* =============================== MODAL =============================== */
dialog {
    background: var(--panel); color: var(--text);
    border: 1.5px solid var(--accent); border-radius: var(--r-panel);
    padding: var(--s4); max-width: 520px; width: 92%;
    max-height: calc(100dvh - (2 * var(--s2))); overflow-y: auto;
    box-shadow: 0 12px 32px rgba(0,0,0,0.55);
}
dialog[open] { animation: settle var(--dur-slow) var(--ease); }
dialog::backdrop { background: rgba(0,0,0,0.72); }
.modal-content h2 { margin-top: 0; color: var(--text); letter-spacing: 0.02em; }
fieldset { border: 1.5px solid var(--border); margin-bottom: var(--s3); border-radius: var(--r-sm); padding: var(--s3); }
legend { padding: 0 10px; font-weight: 700; color: var(--accent); letter-spacing: 0.04em; }
.radio-group label {
    display: flex; align-items: center; margin: 4px 0; font-size: 1.05rem;
    cursor: pointer; padding: 10px; border-radius: var(--r-sm);
    transition: background-color var(--dur) var(--ease);
}
.radio-group label:hover { background: var(--key-hi); }
.radio-group input { transform: scale(1.5); margin-right: 14px; accent-color: var(--accent); }
.setting-help { margin: 0 0 var(--s2); color: var(--text-dim); line-height: 1.5; }
.text-size-controls { display: grid; grid-template-columns: 56px 1fr 56px; align-items: center; gap: var(--s2); }
.text-size-controls output { text-align: center; font-family: var(--font-readout); font-weight: 700; color: var(--text); }

/* =============================== ANIMATIONS =============================== */
@keyframes settle {
    0% { transform: scale(1.04); opacity: 0.6; }
    100% { transform: scale(1); opacity: 1; }
}
/* =============================== RESPONSIVE =============================== */
@media (max-width: 430px) {
    .container {
        padding:
            max(var(--s2), env(safe-area-inset-top))
            max(var(--s2), env(safe-area-inset-right))
            max(var(--s2), env(safe-area-inset-bottom))
            max(var(--s2), env(safe-area-inset-left));
    }
    .app-title { font-size: 0.95rem; }
    .app-title .mark, .app-tag { display: none; }
    .hud-btn { padding-inline: 9px; }
    .keypad-grid { gap: 7px; }
    .btn { min-height: 54px; font-size: 1.25rem; }
    .btn.digit, .btn.op { font-size: 1.55rem; }
    .btn.sci { font-size: 1.05rem; }
    .display-container { min-height: 122px; padding: 12px; }
    #visual-display { font-size: 1.15rem; }
    #result-display { font-size: 2.25rem; }
    .tab-btn { min-width: 82px; font-size: 0.78rem; padding: 9px 10px; }
    .matrix-grid input { width: 52px; height: 52px; }
    .row { flex-wrap: wrap; gap: var(--s2); }
    .half-box { min-width: min(100%, 120px); }
}

@media (max-width: 639px) {
    body[data-scale="large"] .keypad-grid { grid-template-columns: repeat(3, minmax(0, 1fr)); }
    body[data-scale="large"] .keypad-grid.col-2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
    body[data-scale="xlarge"] .keypad-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
    body[data-scale="large"] .hud-bar,
    body[data-scale="xlarge"] .hud-bar { flex-wrap: wrap; }
    body[data-scale="xlarge"] .app-title,
    body[data-scale="xlarge"] .hud-right { width: 100%; }
    body[data-scale="xlarge"] .hud-btn { flex: 1; }
}

@media (min-width: 640px) and (max-width: 919px) {
    .container { max-width: 820px; padding-inline: var(--s4); }
    .tab-bar { display: grid; grid-template-columns: repeat(5, minmax(0, 1fr)); overflow: visible; }
    .tab-btn { min-width: 0; }
    .keypad-grid { gap: 12px; }
    .display-container { min-height: 150px; }
}

@media (min-width: 920px) {
    .tab-bar { display: grid; grid-template-columns: repeat(5, minmax(0, 1fr)); overflow: visible; }
    .tab-btn { min-width: 0; }
    .history[open] { min-height: 150px; }
}

@media (pointer: coarse) {
    .tab-btn, .hud-btn, .tool-btn, .history-clear, .read-btn, .display-tool { min-height: 48px; }
}

@media (forced-colors: active) {
    .btn, .tab-btn, .hud-btn, .tool-btn, .display-container, .history, input, select, dialog {
        forced-color-adjust: auto;
        border: 1px solid ButtonText;
    }
    .active, .btn.equals { outline: 2px solid Highlight; outline-offset: 1px; }
}

/* =============================== REDUCED MOTION =============================== */
@media (prefers-reduced-motion: reduce) {
    *, *::before, *::after { animation-duration: 0.001ms !important; transition-duration: 0.001ms !important; }
    .btn:active, .hud-btn:active, .tool-btn:active, .full-width:active { transform: none; }
}