:root {
    --bg:       #07090e;
    --surface:  #0f1520;
    --surface2: #141c2e;
    --surface3: #1a2238;
    --purple:   #a78bfa;
    --purple2:  #7c3aed;
    --blue:     #60a5fa;
    --green:    #34d399;
    --orange:   #fb923c;
    --gold:     #facc15;
    --pink:     #f472b6;
    --red:      #f87171;
    --text:     #f1f5f9;
    --muted:    #64748b;
    --border:   rgba(255,255,255,0.06);
    --border2:  rgba(255,255,255,0.10);
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
body { font-family: 'Outfit', sans-serif; background: var(--bg); color: var(--text); height: 100vh; overflow: hidden; }

/* ══ NAV ══ */
#phet-stage {
    position: absolute; top: 0; left: 0;
    width: 1280px; height: 720px;
    background: var(--bg);
    display: flex; flex-direction: column;
    overflow: hidden; transform-origin: 0 0;
    box-shadow: 0 0 50px rgba(0, 0, 0, 0.4);
    touch-action: none;
}

.gp-nav {
    position: absolute; top: 0; left: 0; right: 0; height: 54px; z-index: 200;
    display: flex; align-items: center; justify-content: space-between; padding: 0 1.4rem;
    background: rgba(7,9,14,0.96); backdrop-filter: blur(20px);
    border-bottom: 1px solid var(--border);
}
.nav-logo a { text-decoration: none; font-weight: 800; font-size: 1.05rem; color: var(--text); display: flex; align-items: center; gap: 0.4rem; }
.nav-logo em { color: var(--purple); font-style: normal; }
.nav-center { font-size: 0.82rem; color: var(--muted); font-weight: 500; }
.nav-back { display: flex; align-items: center; gap: 0.4rem; padding: 0.38rem 0.9rem; border-radius: 50px; border: 1px solid var(--border); color: var(--text); text-decoration: none; font-size: 0.78rem; transition: 0.2s; }
.nav-back:hover { border-color: var(--purple); color: var(--purple); }

/* ══ LAYOUT ══ */
.app-layout {
    position: absolute; top: 54px; bottom: 0; left: 0; right: 0;
    display: grid; grid-template-columns: 290px 1fr;
}

/* ══ SIDEBAR ══ */
.sidebar {
    display: flex; flex-direction: column;
    background: var(--surface); border-right: 1px solid var(--border);
    overflow: hidden; /* tabs handle their own scroll */
}

/* ── Tab bar ── */
.tab-bar {
    display: flex; border-bottom: 1px solid var(--border);
    background: var(--bg); flex-shrink: 0;
}
.tab-btn {
    flex: 1; display: flex; flex-direction: column; align-items: center; gap: 3px;
    padding: 0.6rem 0.3rem; background: transparent; border: none; cursor: pointer;
    color: var(--muted); font-family: 'Outfit'; font-size: 0.68rem; font-weight: 600;
    text-transform: uppercase; letter-spacing: 0.5px; border-bottom: 2px solid transparent;
    transition: color 0.2s, border-color 0.2s; line-height: 1;
}
.tab-btn i { font-size: 0.9rem; }
.tab-btn:hover { color: var(--text); }
.tab-btn.active { color: var(--purple); border-bottom-color: var(--purple); }

/* ── Tab panels ── */
.tab-panel { display: none; flex-direction: column; flex: 1; overflow: hidden; }
.tab-panel.active { display: flex; }

.panel-body {
    flex: 1; overflow-y: auto; padding: 1rem 1.1rem;
    scrollbar-width: thin; scrollbar-color: var(--surface3) transparent;
}
.panel-body::-webkit-scrollbar { width: 3px; }
.panel-body::-webkit-scrollbar-thumb { background: var(--surface3); border-radius: 3px; }

.panel-hint {
    font-size: 0.78rem; color: var(--muted); margin-bottom: 0.9rem; line-height: 1.6;
    background: var(--surface2); padding: 0.55rem 0.8rem; border-radius: 8px;
    border-left: 3px solid var(--purple);
}
.panel-hint code { font-family: 'JetBrains Mono'; color: var(--purple); font-size: 0.82rem; }

/* ══ FUNCTION INPUTS ══ */
#fnList { display: flex; flex-direction: column; gap: 0.55rem; margin-bottom: 0.8rem; }

.fn-row {
    display: flex; align-items: center; gap: 6px;
    animation: slideIn 0.25s ease;
}
@keyframes slideIn { from { opacity: 0; transform: translateY(-5px); } to { opacity: 1; transform: translateY(0); } }

.fn-color-dot {
    width: 11px; height: 11px; border-radius: 50%; flex-shrink: 0;
    border: 2px solid rgba(255,255,255,0.15); cursor: default;
}
.fn-label {
    font-family: 'JetBrains Mono'; font-size: 0.75rem; color: var(--muted);
    flex-shrink: 0; min-width: 48px;
}
.fn-input {
    flex: 1; min-width: 0;
    background: var(--surface2); border: 1.5px solid var(--border2);
    border-radius: 7px; padding: 0.45rem 0.6rem;
    color: var(--text); font-family: 'JetBrains Mono'; font-size: 0.82rem;
    outline: none; transition: border-color 0.15s, background 0.15s;
}
.fn-input:focus { border-color: var(--purple); background: var(--surface3); }
.fn-input.error { border-color: var(--red); background: rgba(248,113,113,0.05); }
.fn-input.valid { border-color: var(--green); }

.fn-icon-btn {
    width: 26px; height: 26px; flex-shrink: 0; border-radius: 6px;
    border: 1px solid var(--border); background: transparent; color: var(--muted);
    cursor: pointer; display: flex; align-items: center; justify-content: center;
    font-size: 0.7rem; transition: 0.18s;
}
.fn-icon-btn:hover { border-color: var(--border2); color: var(--text); background: var(--surface3); }
.fn-icon-btn.hidden-fn { opacity: 0.28; }
.fn-icon-btn.del:hover { border-color: var(--red); color: var(--red); background: rgba(248,113,113,0.07); }

.add-fn-btn {
    width: 100%; padding: 0.52rem; display: flex; align-items: center; justify-content: center; gap: 0.4rem;
    border: 1.5px dashed rgba(167,139,250,0.3); border-radius: 8px;
    background: transparent; color: var(--purple); font-family: 'Outfit'; font-size: 0.82rem; font-weight: 600;
    cursor: pointer; transition: 0.2s;
}
.add-fn-btn:hover { border-color: var(--purple); background: rgba(167,139,250,0.07); }

/* Active function summary strip */
.fn-summary {
    border-top: 1px solid var(--border); padding: 0.55rem 1.1rem;
    font-size: 0.72rem; color: var(--muted); min-height: 32px;
    display: flex; align-items: center; gap: 0.5rem; flex-wrap: wrap; flex-shrink: 0;
}
.fn-chip {
    display: inline-flex; align-items: center; gap: 4px;
    background: var(--surface2); border: 1px solid var(--border);
    border-radius: 50px; padding: 0.15rem 0.6rem; font-family: 'JetBrains Mono'; font-size: 0.72rem;
}

/* ══ PRESETS TAB ══ */
.category-filter {
    display: flex; gap: 6px; margin-bottom: 0.8rem; flex-wrap: wrap;
}
.cat-btn {
    padding: 0.28rem 0.75rem; border-radius: 50px; border: 1px solid var(--border2);
    background: transparent; color: var(--muted); font-family: 'Outfit'; font-size: 0.75rem;
    font-weight: 600; cursor: pointer; transition: 0.18s;
}
.cat-btn:hover { color: var(--text); border-color: var(--purple); }
.cat-btn.active { background: var(--purple); border-color: var(--purple); color: white; }

.preset-grid { display: flex; flex-direction: column; gap: 0.4rem; }

.preset-btn {
    display: flex; align-items: center; gap: 0.7rem; padding: 0.55rem 0.8rem;
    background: var(--surface2); border: 1px solid var(--border); border-radius: 9px;
    cursor: pointer; transition: 0.18s; text-align: left; width: 100%;
}
.preset-btn:hover { border-color: var(--purple); background: rgba(167,139,250,0.07); transform: translateX(2px); }
.preset-icon { font-size: 1.1rem; flex-shrink: 0; width: 28px; text-align: center; }
.preset-info { flex: 1; min-width: 0; }
.preset-fn { font-family: 'JetBrains Mono'; font-size: 0.82rem; color: var(--purple); font-weight: 600; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; display: block; }
.preset-name { font-size: 0.72rem; color: var(--muted); display: block; }

/* ══ VIEW TAB ══ */
.view-group { margin-bottom: 1rem; }
.view-group-label { font-size: 0.7rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.8px; color: var(--muted); margin-bottom: 0.45rem; }
.range-row { display: flex; align-items: center; gap: 0.5rem; }
.range-inp {
    flex: 1; background: var(--surface2); border: 1.5px solid var(--border2);
    border-radius: 7px; padding: 0.45rem 0.6rem; color: var(--text);
    font-family: 'JetBrains Mono'; font-size: 0.85rem;
    outline: none; text-align: center; -moz-appearance: textfield; appearance: textfield;
}
.range-inp::-webkit-outer-spin-button,
.range-inp::-webkit-inner-spin-button { -webkit-appearance: none; }
.range-inp:focus { border-color: var(--purple); }
.range-arrow { color: var(--muted); font-size: 0.85rem; }

.view-btn-row { display: flex; gap: 0.5rem; margin-bottom: 1rem; }
.vbtn {
    flex: 1; padding: 0.5rem; border-radius: 8px; font-family: 'Outfit'; font-size: 0.8rem;
    font-weight: 600; cursor: pointer; transition: 0.18s; display: flex; align-items: center; justify-content: center; gap: 0.35rem; border: 1px solid transparent;
}
.vbtn.primary { background: var(--purple); color: white; border-color: var(--purple); }
.vbtn.primary:hover { background: var(--purple2); }
.vbtn.ghost { background: transparent; border-color: var(--border2); color: var(--muted); }
.vbtn.ghost:hover { border-color: var(--text); color: var(--text); }

.separator { height: 1px; background: var(--border); margin: 0.8rem 0; }

.quick-views { display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem; margin-bottom: 0.5rem; }
.qv-btn {
    padding: 0.4rem; border-radius: 7px; border: 1px solid var(--border);
    background: var(--surface2); color: var(--muted); font-family: 'JetBrains Mono'; font-size: 0.72rem;
    cursor: pointer; transition: 0.18s; text-align: center;
}
.qv-btn:hover { border-color: var(--blue); color: var(--blue); background: rgba(96,165,250,0.06); }

.toggle-row {
    display: flex; align-items: center; justify-content: space-between;
    padding: 0.45rem 0; border-bottom: 1px solid var(--border); cursor: pointer;
    font-size: 0.85rem; color: #94a3b8;
}
.toggle-row:last-of-type { border-bottom: none; }
.toggle-check { accent-color: var(--purple); width: 16px; height: 16px; cursor: pointer; }

/* ══ REF TAB ══ */
.ref-section-title {
    font-size: 0.68rem; font-weight: 700; text-transform: uppercase; letter-spacing: 1px;
    color: var(--muted); margin: 0.9rem 0 0.4rem;
    padding-bottom: 0.3rem; border-bottom: 1px solid var(--border);
}
.ref-section-title:first-child { margin-top: 0; }
.ref-table { display: flex; flex-direction: column; gap: 2px; }
.ref-row {
    display: flex; align-items: center; justify-content: space-between;
    padding: 0.32rem 0.6rem; border-radius: 6px; background: var(--surface2);
}
.ref-row code { font-family: 'JetBrains Mono'; font-size: 0.8rem; color: var(--gold); }
.ref-row span { font-size: 0.72rem; color: var(--muted); }
.ref-row.clickable-ref { cursor: pointer; transition: 0.15s; }
.ref-row.clickable-ref:hover { background: rgba(167,139,250,0.1); border-radius: 6px; }
.ref-row.clickable-ref:hover code { color: var(--purple); }
.ref-row.clickable-ref:hover span::before { content: '↩ insert · '; color: var(--purple); font-size: 0.65rem; }

/* ══ GRAPH AREA ══ */
.graph-area { position: relative; background: var(--bg); overflow: hidden; }
#graphCanvas { display: block; width: 100%; height: 100%; cursor: crosshair; }
#graphCanvas.panning { cursor: grabbing; }

/* ── Zoom buttons ── */
.zoom-controls { position: absolute; bottom: 44px; right: 14px; display: flex; flex-direction: column; gap: 4px; }
.zoom-btn {
    width: 36px; height: 36px; border-radius: 9px;
    background: rgba(15,21,32,0.92); border: 1px solid var(--border2);
    color: var(--text); font-size: 0.8rem; cursor: pointer;
    display: flex; align-items: center; justify-content: center;
    transition: 0.18s; backdrop-filter: blur(8px);
}
.zoom-btn:hover { border-color: var(--purple); color: var(--purple); background: rgba(167,139,250,0.08); }

/* ── Coord tooltip ── */
.coord-tooltip {
    position: absolute; background: rgba(15,21,32,0.96); border: 1px solid var(--border2);
    border-radius: 8px; padding: 0.4rem 0.75rem; font-family: 'JetBrains Mono'; font-size: 0.76rem;
    color: var(--text); pointer-events: none; display: none; backdrop-filter: blur(8px);
    white-space: nowrap; box-shadow: 0 4px 24px rgba(0,0,0,0.4); z-index: 10;
}

/* ── Status bar ── */
.status-bar {
    position: absolute; bottom: 0; left: 0; right: 0; height: 34px;
    background: rgba(15,21,32,0.96); border-top: 1px solid var(--border);
    display: flex; align-items: center; justify-content: space-between;
    padding: 0 0.9rem; font-size: 0.72rem; color: var(--muted); backdrop-filter: blur(8px);
}
#coordDisplay { display: flex; align-items: center; gap: 0.4rem; }
#scaleDisplay { font-family: 'JetBrains Mono'; font-size: 0.68rem; color: var(--surface3); opacity: 0.7; }