*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --paper: #f7f5f0;
  --paper-bright: #fdfcfa;
  --paper-shadow: #e8e4dc;
  --ink: #1a1a1a;
  --ink-muted: #5a5a5a;
  --ink-light: #8a8580;
  --rule: #d8d4cc;
  --rule-dark: #c4bfb6;
  --accent: #1a4d7a;
  --accent-hover: #2563a8;
  --calc-body: #eceae4;
  --calc-border: #c8c4bc;
  --lcd-bg: #e8f0e6;
  --lcd-text: #1a3d2a;
  --lcd-dim: #3d6b52;
  --key-num-top: #ffffff;
  --key-num-face: #f0eeea;
  --key-num-shadow: #b8b4ac;
  --key-op-top: #3a7bc8;
  --key-op-face: #2563b0;
  --key-op-shadow: #1a4a8a;
  --key-fn-top: #e8e6e2;
  --key-fn-face: #d8d6d0;
  --key-fn-shadow: #a8a49c;
  --key-shift-top: #e07a30;
  --key-shift-face: #c86520;
  --key-shift-shadow: #8a4010;
  --key-eq-top: #3aab6e;
  --key-eq-face: #2a9458;
  --key-eq-shadow: #1a6b3a;
  --mono: 'JetBrains Mono', monospace;
  --sans: 'Inter', system-ui, Georgia, serif;
}

html, body {
  min-height: 100%;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 14px;
  line-height: 1.5;
}

body {
  background:
    linear-gradient(180deg, var(--paper-bright) 0%, var(--paper) 100%);
}

.app {
  max-width: 1100px;
  margin: 0 auto;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  background: var(--paper-bright);
  box-shadow: 0 0 60px rgba(0,0,0,0.06);
}

/* ── Shared 3D button base ── */
.btn-3d {
  position: relative;
  cursor: pointer;
  border: 1px solid var(--rule-dark);
  transition: transform 0.07s ease, box-shadow 0.07s ease;
  user-select: none;
  -webkit-tap-highlight-color: transparent;
}
.btn-3d:hover { filter: brightness(1.03); }
.btn-3d:active,
.btn-3d.pressed {
  transform: translateY(3px) !important;
  filter: brightness(0.97);
}

/* Header */
.header {
  display: flex;
  align-items: center;
  gap: 16px;
  padding: 14px 24px;
  background: var(--paper-bright);
  border-bottom: 2px solid var(--ink);
  flex-wrap: wrap;
}
.brand { display: flex; align-items: baseline; gap: 10px; flex-wrap: wrap; }
.brand-mark {
  font-size: 9px;
  font-weight: 700;
  color: var(--accent);
  letter-spacing: 0.12em;
  text-transform: uppercase;
}
.brand h1 {
  font-size: 20px;
  font-weight: 700;
  color: var(--ink);
  font-family: Georgia, 'Times New Roman', serif;
}
.model {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--ink-muted);
}

.mode-tabs { display: flex; gap: 6px; flex: 1; justify-content: center; flex-wrap: wrap; }
.tab {
  font-family: var(--sans);
  font-size: 12px;
  font-weight: 600;
  padding: 9px 18px;
  border-radius: 6px;
  color: var(--ink-muted);
  background: linear-gradient(180deg, #fff 0%, var(--paper-shadow) 100%);
  box-shadow: 0 3px 0 var(--rule-dark), 0 4px 8px rgba(0,0,0,0.06);
}
.tab:hover { color: var(--ink); }
.tab:active, .tab.pressed {
  box-shadow: 0 1px 0 var(--rule-dark), 0 2px 4px rgba(0,0,0,0.04);
}
.tab.active {
  background: linear-gradient(180deg, #fff 0%, #e8eef5 100%);
  color: var(--accent);
  border-color: var(--accent);
  box-shadow: 0 3px 0 var(--accent), 0 4px 10px rgba(26,77,122,0.15);
}
.tab.active:active, .tab.active.pressed {
  box-shadow: 0 1px 0 var(--accent);
}

.angle-toggle { display: flex; gap: 4px; }
.angle-btn {
  font-family: var(--mono);
  font-size: 11px;
  font-weight: 600;
  padding: 7px 14px;
  border-radius: 5px;
  color: var(--ink-muted);
  background: linear-gradient(180deg, #fff, var(--paper-shadow));
  box-shadow: 0 2px 0 var(--rule-dark);
}
.angle-btn:active, .angle-btn.pressed { box-shadow: 0 0 0 var(--rule-dark); }
.angle-btn.active {
  background: linear-gradient(180deg, var(--key-op-top), var(--key-op-face));
  color: #fff;
  border-color: var(--key-op-shadow);
  box-shadow: 0 3px 0 var(--key-op-shadow);
}
.angle-btn.active:active, .angle-btn.active.pressed {
  box-shadow: 0 1px 0 var(--key-op-shadow);
}

/* Main panels */
.main {
  flex: 1;
  padding: 24px;
  background: var(--paper);
  border-left: 1px solid var(--rule);
  border-right: 1px solid var(--rule);
}
.panel { display: none; }
.panel.active { display: block; }

/* ═══ CALCULATE ═══ */
.calc-unit {
  max-width: 480px;
  margin: 0 auto;
  background: linear-gradient(180deg, #f5f3ee 0%, var(--calc-body) 100%);
  border-radius: 14px;
  padding: 20px;
  box-shadow:
    0 1px 0 #fff inset,
    0 6px 0 var(--calc-border),
    0 10px 30px rgba(0,0,0,0.1);
  border: 2px solid var(--calc-border);
}

.lcd {
  background: var(--lcd-bg);
  border-radius: 8px;
  padding: 14px 18px;
  margin-bottom: 16px;
  border: 2px solid var(--rule-dark);
  min-height: 100px;
  box-shadow: inset 0 2px 8px rgba(0,0,0,0.06);
}
.lcd-mode {
  font-family: var(--mono);
  font-size: 10px;
  color: var(--lcd-dim);
  margin-bottom: 4px;
  letter-spacing: 0.05em;
}
.lcd-history {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--ink-light);
  text-align: right;
  min-height: 16px;
}
.lcd-input {
  font-family: var(--mono);
  font-size: 1.5rem;
  font-weight: 600;
  color: var(--lcd-text);
  text-align: right;
  word-break: break-all;
}
.lcd-result {
  font-family: var(--mono);
  font-size: 1.1rem;
  color: var(--lcd-dim);
  text-align: right;
  min-height: 24px;
  border-top: 1px solid var(--rule);
  margin-top: 8px;
  padding-top: 8px;
}

.keypad {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 8px;
}

.key {
  font-family: var(--mono);
  font-size: 12px;
  font-weight: 600;
  border: 1px solid transparent;
  border-radius: 8px;
  padding: 13px 4px;
  cursor: pointer;
  position: relative;
  min-height: 44px;
  transition: transform 0.07s ease, box-shadow 0.07s ease;
  user-select: none;
  -webkit-tap-highlight-color: transparent;
}
.key::before {
  content: '';
  position: absolute;
  inset: 0;
  border-radius: 7px;
  background: linear-gradient(180deg, rgba(255,255,255,0.5) 0%, transparent 45%);
  pointer-events: none;
}
.key:hover { filter: brightness(1.04); }
.key:active,
.key.pressed {
  transform: translateY(4px);
  filter: brightness(0.96);
}

.key .shift-label {
  position: absolute;
  top: 4px; left: 6px;
  font-size: 8px;
  font-weight: 700;
  opacity: 0.85;
  z-index: 1;
}

.key-num {
  background: linear-gradient(180deg, var(--key-num-top), var(--key-num-face));
  color: var(--ink);
  box-shadow: 0 4px 0 var(--key-num-shadow), 0 6px 10px rgba(0,0,0,0.08);
  border-color: var(--rule);
}
.key-num:active, .key-num.pressed {
  box-shadow: 0 1px 0 var(--key-num-shadow), 0 2px 4px rgba(0,0,0,0.06);
}

.key-op {
  background: linear-gradient(180deg, var(--key-op-top), var(--key-op-face));
  color: #fff;
  font-size: 15px;
  box-shadow: 0 4px 0 var(--key-op-shadow), 0 6px 10px rgba(26,77,122,0.2);
  border-color: var(--key-op-shadow);
}
.key-op:active, .key-op.pressed {
  box-shadow: 0 1px 0 var(--key-op-shadow), 0 2px 4px rgba(26,77,122,0.15);
}

.key-fn {
  background: linear-gradient(180deg, var(--key-fn-top), var(--key-fn-face));
  color: var(--ink-muted);
  font-size: 11px;
  box-shadow: 0 4px 0 var(--key-fn-shadow), 0 5px 8px rgba(0,0,0,0.07);
  border-color: var(--rule-dark);
}
.key-fn:active, .key-fn.pressed {
  box-shadow: 0 1px 0 var(--key-fn-shadow);
}
.key-fn .shift-label { color: var(--key-shift-face); }

.key-shift {
  background: linear-gradient(180deg, var(--key-shift-top), var(--key-shift-face));
  color: #fff;
  box-shadow: 0 4px 0 var(--key-shift-shadow), 0 6px 10px rgba(138,64,16,0.2);
  border-color: var(--key-shift-shadow);
}
.key-shift:active, .key-shift.pressed {
  box-shadow: 0 1px 0 var(--key-shift-shadow);
}
.key-shift .shift-label { color: rgba(255,255,255,0.7); }

.key-eq {
  background: linear-gradient(180deg, var(--key-eq-top), var(--key-eq-face));
  color: #fff;
  font-size: 18px;
  box-shadow: 0 4px 0 var(--key-eq-shadow), 0 6px 10px rgba(26,107,58,0.2);
  border-color: var(--key-eq-shadow);
}
.key-eq:active, .key-eq.pressed {
  box-shadow: 0 1px 0 var(--key-eq-shadow);
}

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

/* ═══ GRAPH ═══ */
.graph-layout {
  display: grid;
  grid-template-columns: 280px 1fr;
  gap: 20px;
  min-height: 420px;
}
@media (max-width: 700px) {
  .graph-layout { grid-template-columns: 1fr; }
}

.graph-controls, .solve-controls, .stats-controls {
  background: var(--paper-bright);
  border: 1px solid var(--rule);
  border-radius: 10px;
  padding: 18px;
  box-shadow: 0 2px 8px rgba(0,0,0,0.04);
}
.graph-controls h3, .solve-controls h3, .stats-controls h3 {
  font-size: 15px;
  margin-bottom: 6px;
  color: var(--ink);
  font-family: Georgia, serif;
  border-bottom: 1px solid var(--rule);
  padding-bottom: 8px;
}
.panel-desc {
  font-size: 12px;
  color: var(--ink-muted);
  margin-bottom: 14px;
  line-height: 1.6;
}

.expr-input, input[type="number"], input[type="text"], textarea {
  width: 100%;
  background: #fff;
  border: 1px solid var(--rule-dark);
  border-radius: 6px;
  padding: 9px 11px;
  color: var(--ink);
  font-family: var(--mono);
  font-size: 12px;
  margin-top: 4px;
  box-shadow: inset 0 1px 3px rgba(0,0,0,0.05);
}
.expr-input:focus, input:focus, textarea:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: inset 0 1px 3px rgba(0,0,0,0.05), 0 0 0 2px rgba(26,77,122,0.12);
}
label { display: block; font-size: 12px; color: var(--ink-muted); margin-bottom: 10px; font-weight: 500; }

.range-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px;
  margin: 12px 0;
}
.range-grid label { margin: 0; font-size: 11px; }
.range-grid input { margin-top: 2px; }

.btn-row { display: flex; gap: 10px; margin: 14px 0; }

.action-btn {
  flex: 1;
  padding: 11px 14px;
  font-weight: 600;
  border-radius: 7px;
  cursor: pointer;
  font-family: var(--sans);
  font-size: 13px;
  background: linear-gradient(180deg, var(--key-eq-top), var(--key-eq-face));
  color: #fff;
  border: 1px solid var(--key-eq-shadow);
  box-shadow: 0 4px 0 var(--key-eq-shadow), 0 5px 10px rgba(26,107,58,0.15);
  transition: transform 0.07s, box-shadow 0.07s;
}
.action-btn:hover { filter: brightness(1.05); }
.action-btn:active, .action-btn.pressed {
  transform: translateY(3px);
  box-shadow: 0 1px 0 var(--key-eq-shadow);
}
.action-btn.secondary {
  background: linear-gradient(180deg, #fff, var(--paper-shadow));
  color: var(--ink);
  border-color: var(--rule-dark);
  box-shadow: 0 3px 0 var(--rule-dark);
}
.action-btn.secondary:active, .action-btn.secondary.pressed {
  box-shadow: 0 1px 0 var(--rule-dark);
}

.preset-row {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  align-items: center;
  font-size: 11px;
  color: var(--ink-muted);
  margin-top: 12px;
}
.preset-btn {
  padding: 6px 12px;
  background: linear-gradient(180deg, #fff, var(--paper-shadow));
  border: 1px solid var(--rule-dark);
  color: var(--ink);
  border-radius: 5px;
  cursor: pointer;
  font-family: var(--mono);
  font-size: 10px;
  font-weight: 500;
  box-shadow: 0 2px 0 var(--rule-dark);
  transition: transform 0.07s, box-shadow 0.07s;
}
.preset-btn:hover { border-color: var(--accent); color: var(--accent); }
.preset-btn:active, .preset-btn.pressed {
  transform: translateY(2px);
  box-shadow: 0 0 0 var(--rule-dark);
}

.graph-canvas-wrap {
  background: #fff;
  border: 1px solid var(--rule-dark);
  border-radius: 10px;
  overflow: hidden;
  min-height: 360px;
  box-shadow: inset 0 1px 4px rgba(0,0,0,0.04), 0 2px 8px rgba(0,0,0,0.04);
}
#graph-canvas { display: block; width: 100%; height: 100%; min-height: 360px; }

/* ═══ SOLVE & STATS ═══ */
.solve-layout, .stats-layout {
  display: grid;
  grid-template-columns: 300px 1fr;
  gap: 20px;
}
@media (max-width: 700px) {
  .solve-layout, .stats-layout { grid-template-columns: 1fr; }
}

.solve-type-tabs, .stats-type-tabs {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-bottom: 14px;
}
.solve-tab, .stats-tab {
  padding: 7px 12px;
  font-size: 11px;
  font-weight: 600;
  background: linear-gradient(180deg, #fff, var(--paper-shadow));
  border: 1px solid var(--rule-dark);
  color: var(--ink-muted);
  border-radius: 5px;
  cursor: pointer;
  box-shadow: 0 2px 0 var(--rule-dark);
  transition: transform 0.07s, box-shadow 0.07s;
}
.solve-tab:hover, .stats-tab:hover { color: var(--ink); }
.solve-tab:active, .stats-tab:active,
.solve-tab.pressed, .stats-tab.pressed {
  transform: translateY(2px);
  box-shadow: 0 0 0 var(--rule-dark);
}
.solve-tab.active, .stats-tab.active {
  background: linear-gradient(180deg, #e8f0fa, #d0e0f0);
  color: var(--accent);
  border-color: var(--accent);
  box-shadow: 0 3px 0 var(--accent);
}
.solve-tab.active:active, .stats-tab.active:active,
.solve-tab.active.pressed, .stats-tab.active.pressed {
  box-shadow: 0 1px 0 var(--accent);
}

.solve-form, .stats-form { display: none; }
.solve-form.active, .stats-form.active { display: block; }
.solve-form p { font-size: 12px; color: var(--ink-muted); margin-bottom: 10px; line-height: 1.6; }

.coef-row {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 8px;
}
.coef-row label { margin: 0; min-width: 80px; font-size: 12px; }
.coef-row input { flex: 1; margin: 0; }

.solve-output, .stats-output {
  background: var(--paper-bright);
  border: 1px solid var(--rule);
  border-radius: 10px;
  padding: 18px;
  overflow: auto;
  box-shadow: 0 2px 8px rgba(0,0,0,0.04);
}
.solve-output h4, .stats-output h4 {
  font-size: 11px;
  color: var(--ink-muted);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin-bottom: 12px;
  font-weight: 600;
}
#solve-steps, #stats-results {
  font-family: var(--mono);
  font-size: 12px;
  line-height: 1.75;
  color: var(--ink);
  white-space: pre-wrap;
  word-break: break-word;
}

textarea { resize: vertical; min-height: 60px; }

.footer {
  padding: 12px 24px;
  font-size: 10px;
  color: var(--ink-light);
  border-top: 2px solid var(--ink);
  background: var(--paper-bright);
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 8px;
  font-family: var(--mono);
}