:root {
    /* palette */
    --bg:          #15171a;
    --toolbar-bg:  #1d2024;
    --tab-bg:      #1a1d20;
    --panel-bg:    #0c0d0f;
    --border:      #2c3035;
    --border-soft: #23272c;
    --fg:          #d6d9dd;
    --fg-dim:      #8a9099;
    --fg-mute:     #5f666f;
    --accent:      #3b82f6;
    --accent-dim:  #2b5fb0;
    --danger:      #ef4444;
    --ok:          #22c55e;

    /* spacing scale (8px base) */
    --s-1: 4px;
    --s-2: 8px;
    --s-3: 12px;
    --s-4: 16px;
    --s-5: 24px;

    --ctrl-h: 30px;
    --radius: 5px;
    --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    --mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
}

* { box-sizing: border-box; }

html, body {
    margin: 0;
    padding: 0;
    background: var(--bg);
    color: var(--fg);
    font-family: var(--font);
    font-size: 13px;
    height: 100%;
    overflow: hidden;
    -webkit-font-smoothing: antialiased;
}

/* ---------- toolbar ---------- */
#toolbar {
    display: flex;
    align-items: center;
    gap: var(--s-2);
    padding: var(--s-2) var(--s-3);
    background: var(--toolbar-bg);
    border-bottom: 1px solid var(--border);
    flex-wrap: wrap;
    min-height: 46px;
}

.brand {
    font-weight: 600;
    font-size: 14px;
    letter-spacing: .3px;
    color: var(--fg);
    padding-right: var(--s-2);
    user-select: none;
}
.brand::before {
    content: "";
    display: inline-block;
    width: 8px; height: 8px;
    border-radius: 50%;
    background: var(--accent);
    margin-right: var(--s-2);
    vertical-align: middle;
}

.group {
    display: flex;
    align-items: center;
    gap: var(--s-2);
}

.divider {
    width: 1px;
    align-self: stretch;
    background: var(--border);
    margin: 2px var(--s-1);
}

.spacer { flex: 1; }

#toolbar label {
    display: flex;
    align-items: center;
    gap: var(--s-1);
    color: var(--fg-dim);
    font-size: 12px;
    white-space: nowrap;
}

#toolbar input[type=number],
#toolbar select {
    height: var(--ctrl-h);
    width: 72px;
    padding: 0 var(--s-2);
    background: var(--panel-bg);
    color: var(--fg);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    font: inherit;
    font-family: var(--mono);
    outline: none;
    transition: border-color .12s, box-shadow .12s;
}
#toolbar input[type=number]:focus,
#toolbar select:focus {
    border-color: var(--accent-dim);
    box-shadow: 0 0 0 2px rgba(59,130,246,.18);
}
#toolbar select { width: auto; cursor: pointer; }

/* buttons */
#toolbar button,
#ps-buttons button {
    height: var(--ctrl-h);
    padding: 0 var(--s-3);
    background: var(--panel-bg);
    color: var(--fg);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    font: inherit;
    cursor: pointer;
    transition: background .12s, border-color .12s, color .12s;
    white-space: nowrap;
}
#toolbar button:hover,
#ps-buttons button:hover {
    background: #262a2f;
    border-color: #3a3f45;
}
#toolbar button:active,
#ps-buttons button:active { background: #1a1d20; }
#toolbar button.primary {
    background: var(--accent);
    border-color: var(--accent);
    color: #fff;
    font-weight: 500;
}
#toolbar button.primary:hover {
    background: var(--accent-dim);
    border-color: var(--accent-dim);
}
#toolbar button:disabled,
#ps-buttons button:disabled {
    opacity: .4;
    cursor: not-allowed;
}

#toolbar .check {
    flex-direction: row;
    gap: var(--s-1);
    color: var(--fg);
    cursor: pointer;
    user-select: none;
}
#toolbar .check input { accent-color: var(--accent); }

.status {
    font-size: 12px;
    color: var(--fg-dim);
    min-width: 90px;
    text-align: right;
    font-family: var(--mono);
}
.status::before {
    content: "";
    display: inline-block;
    width: 7px; height: 7px;
    border-radius: 50%;
    background: var(--fg-mute);
    margin-right: var(--s-1);
    vertical-align: middle;
}

/* ---------- tabs ---------- */
#tabs {
    display: flex;
    background: var(--tab-bg);
    border-bottom: 1px solid var(--border);
    padding: var(--s-1) var(--s-2) 0;
    min-height: 34px;
    overflow-x: auto;
    scrollbar-width: thin;
}
.tab {
    display: flex;
    align-items: center;
    gap: var(--s-2);
    padding: var(--s-1) var(--s-3);
    cursor: pointer;
    font-size: 12px;
    color: var(--fg-dim);
    border: 1px solid transparent;
    border-bottom: none;
    border-radius: var(--radius) var(--radius) 0 0;
    user-select: none;
    white-space: nowrap;
    margin-right: 2px;
}
.tab:hover { color: var(--fg); background: rgba(255,255,255,.03); }
.tab.active {
    color: var(--fg);
    background: var(--bg);
    border-color: var(--border);
    border-bottom: 1px solid var(--bg);
    margin-bottom: -1px;
}
.tab .close {
    font-size: 13px;
    line-height: 1;
    color: var(--fg-mute);
    padding: 0 2px;
    border-radius: 3px;
}
.tab .close:hover { color: var(--danger); background: rgba(239,68,68,.12); }
.tab.dragging { opacity: .4; }

/* ---------- panel / canvases ---------- */
#panel {
    display: flex;
    flex-direction: column;
    height: calc(100vh - 82px);
}
#output {
    width: 100%;
    height: 70px;
    display: block;
    background: #000;
    border-bottom: 1px solid var(--border);
}
#graphs {
    display: flex;
    flex: 1;
    min-height: 0;
}
#paperstrip-wrap {
    width: 320px;
    flex-shrink: 0;
    display: flex;
    flex-direction: column;
    border-right: 1px solid var(--border);
    background: #000;
}
#paperstrip {
    flex: 1;
    width: 100%;
    display: block;
}
#ps-buttons {
    display: flex;
    gap: var(--s-1);
    padding: var(--s-2);
    background: var(--toolbar-bg);
    border-top: 1px solid var(--border);
}
#ps-buttons button {
    flex: 1;
    padding: 0;
    height: 28px;
}
#waveforms {
    flex: 1;
    display: flex;
    flex-direction: column;
    min-width: 0;
}
#waveforms canvas {
    flex: 1;
    width: 100%;
    height: 33.33%;
    display: block;
    background: #000;
    border-bottom: 1px solid var(--border-soft);
}
#waveforms canvas:last-child { border-bottom: none; }

/* ---------- start overlay ---------- */
#start-overlay {
    position: fixed;
    inset: 0;
    background: rgba(10, 11, 13, .88);
    backdrop-filter: blur(4px);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 100;
}
#start-overlay.hidden { display: none; }
#start-overlay .box {
    background: var(--toolbar-bg);
    border: 1px solid var(--border);
    padding: var(--s-5) var(--s-5);
    border-radius: 10px;
    text-align: center;
    max-width: 440px;
    box-shadow: 0 12px 48px rgba(0,0,0,.5);
}
#start-overlay h1 {
    margin: 0 0 var(--s-2);
    font-size: 22px;
    font-weight: 600;
    color: var(--fg);
}
#start-overlay h1::before {
    content: "";
    display: inline-block;
    width: 10px; height: 10px;
    border-radius: 50%;
    background: var(--accent);
    margin-right: var(--s-2);
    vertical-align: middle;
}
#start-overlay p {
    color: var(--fg-dim);
    font-size: 13px;
    line-height: 1.6;
    margin: var(--s-2) 0;
}
#start-overlay button {
    margin: var(--s-3) 0;
    height: 38px;
    padding: 0 var(--s-5);
    font-size: 14px;
    font-weight: 500;
    background: var(--accent);
    color: #fff;
    border: none;
    border-radius: var(--radius);
    cursor: pointer;
    transition: background .12s;
}
#start-overlay button:hover { background: var(--accent-dim); }
#start-overlay .hint { font-size: 11px; color: var(--fg-mute); margin-top: var(--s-1); }
code {
    background: var(--panel-bg);
    border: 1px solid var(--border);
    padding: 1px 5px;
    border-radius: 3px;
    font-family: var(--mono);
    font-size: 11px;
}

/* ---------- scrollbars ---------- */
::-webkit-scrollbar { width: 10px; height: 10px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 5px; border: 2px solid var(--toolbar-bg); }
::-webkit-scrollbar-thumb:hover { background: #3a3f45; }

/* ---------- accessibility: focus visibility ---------- */
:focus { outline: none; }
:focus-visible {
    outline: 2px solid var(--accent);
    outline-offset: 2px;
}
#toolbar button:focus-visible,
#toolbar input:focus-visible,
#toolbar select:focus-visible,
#ps-buttons button:focus-visible {
    outline-offset: 1px;
}
.tab:focus-visible {
    outline: 2px solid var(--accent);
    outline-offset: -2px;
}

/* ---------- responsive: tablet (≤1024px) ---------- */
@media (max-width: 1024px) {
    :root { --s-3: 10px; --s-4: 14px; }
    #paperstrip-wrap { width: 280px; }
    #toolbar { gap: var(--s-1); padding: var(--s-2); }
    .brand { font-size: 13px; }
}

/* ---------- responsive: phone (≤768px) ---------- */
@media (max-width: 768px) {
    html, body {
        font-size: 12px;
        -webkit-text-size-adjust: 100%;
    }
    /* toolbar becomes a single horizontal scroll row */
    #toolbar {
        flex-wrap: nowrap;
        overflow-x: auto;
        scrollbar-width: none;
        gap: var(--s-2);
        padding: var(--s-1) var(--s-2);
        padding-top: max(var(--s-1), env(safe-area-inset-top));
        padding-left: max(var(--s-2), env(safe-area-inset-left));
        padding-right: max(var(--s-2), env(safe-area-inset-right));
    }
    #toolbar::-webkit-scrollbar { display: none; }
    .brand { font-size: 12px; padding-right: var(--s-1); flex-shrink: 0; }
    .divider { display: none; }
    .group { flex-shrink: 0; }
    #toolbar label { font-size: 11px; }
    #toolbar input[type=number] { width: 54px; }
    #toolbar select { width: auto; }
    /* larger touch targets */
    #toolbar button,
    #ps-buttons button {
        min-height: 40px;
        padding: 0 var(--s-3);
    }
    #toolbar input[type=number],
    #toolbar select { height: 40px; }
    .status { min-width: 0; font-size: 11px; }
    #tabs { padding-top: var(--s-1); }
    .tab { padding: var(--s-2) var(--s-3); font-size: 12px; }

    /* panel stacks vertically: output / paperstrip / waveforms */
    #panel { height: calc(100vh - 84px); }
    #output { height: 60px; }
    #graphs { flex-direction: column; }
    #paperstrip-wrap {
        width: 100%;
        height: 40%;
        flex-shrink: 0;
        border-right: none;
        border-bottom: 1px solid var(--border);
    }
    #waveforms { flex: 1; min-height: 0; }
    #waveforms canvas { height: 33.33%; }
}

/* ---------- responsive: small phone (≤480px) ---------- */
@media (max-width: 480px) {
    .brand::before { display: none; }
    .brand { padding-right: 0; }
    #toolbar label { font-size: 10px; gap: 2px; }
    #toolbar input[type=number] { width: 46px; padding: 0 4px; }
    #output { height: 54px; }
}

/* ---------- touch devices: bigger tab close hit area ---------- */
@media (hover: none) and (pointer: coarse) {
    .tab .close { padding: 4px 8px; }
    .tab { padding: var(--s-2) var(--s-3); }
}

/* ---------- landscape phone: give waveforms more room ---------- */
@media (max-width: 900px) and (orientation: landscape) and (max-height: 500px) {
    #paperstrip-wrap { height: 100%; width: 260px; border-bottom: none; border-right: 1px solid var(--border); }
    #graphs { flex-direction: row; }
    #output { height: 50px; }
    #panel { height: calc(100vh - 80px); }
}

/* reduced motion: no transitions */
@media (prefers-reduced-motion: reduce) {
    * { transition: none !important; }
}