/* ========== CSS Variables / Themes ========== */
:root {
  --transition-speed: 0.2s;
}

[data-theme="dark"] {
  --bg-primary: #1a1a2e;
  --bg-secondary: #16213e;
  --bg-panel: #0f3460;
  --bg-btn: #1a1a40;
  --bg-btn-hover: #2a2a5a;
  --bg-btn-active: #3a3a6a;
  --bg-display: #0a0a1a;
  --bg-btn-operator: #e94560;
  --bg-btn-operator-hover: #ff6b81;
  --bg-btn-equals: #00d2ff;
  --bg-btn-equals-hover: #00b8e6;
  --bg-btn-danger: #ff4757;
  --bg-btn-warning: #ffa502;
  --text-primary: #e0e0e0;
  --text-secondary: #a0a0a0;
  --text-result: #00d2ff;
  --text-btn: #ffffff;
  --border-color: #2a2a4a;
  --shadow-color: rgba(0, 0, 0, 0.4);
  --canvas-bg: #0a0a1a;
  --canvas-grid: #1a1a3a;
  --canvas-axis: #4a4a6a;
  --canvas-line: #00d2ff;
  --scrollbar-track: #1a1a2e;
  --scrollbar-thumb: #3a3a5a;
  --history-hover: #1a1a40;
}

[data-theme="light"] {
  --bg-primary: #f0f2f5;
  --bg-secondary: #ffffff;
  --bg-panel: #ffffff;
  --bg-btn: #e8e8e8;
  --bg-btn-hover: #d0d0d0;
  --bg-btn-active: #c0c0c0;
  --bg-display: #ffffff;
  --bg-btn-operator: #4a90d9;
  --bg-btn-operator-hover: #357abd;
  --bg-btn-equals: #2ecc71;
  --bg-btn-equals-hover: #27ae60;
  --bg-btn-danger: #e74c3c;
  --bg-btn-warning: #f39c12;
  --text-primary: #2c3e50;
  --text-secondary: #7f8c8d;
  --text-result: #2ecc71;
  --text-btn: #2c3e50;
  --border-color: #ddd;
  --shadow-color: rgba(0, 0, 0, 0.1);
  --canvas-bg: #fafafa;
  --canvas-grid: #e0e0e0;
  --canvas-axis: #888;
  --canvas-line: #e74c3c;
  --scrollbar-track: #f0f0f0;
  --scrollbar-thumb: #ccc;
  --history-hover: #f5f5f5;
}

[data-theme="retro"] {
  --bg-primary: #2d1b00;
  --bg-secondary: #3e2a10;
  --bg-panel: #4a3520;
  --bg-btn: #5a4530;
  --bg-btn-hover: #6a5540;
  --bg-btn-active: #7a6550;
  --bg-display: #1a0f00;
  --bg-btn-operator: #c8841d;
  --bg-btn-operator-hover: #d9a040;
  --bg-btn-equals: #d4a017;
  --bg-btn-equals-hover: #e8b630;
  --bg-btn-danger: #a03030;
  --bg-btn-warning: #c8841d;
  --text-primary: #d4a060;
  --text-secondary: #8a7050;
  --text-result: #ffd700;
  --text-btn: #f0d0a0;
  --border-color: #5a4530;
  --shadow-color: rgba(0, 0, 0, 0.5);
  --canvas-bg: #1a0f00;
  --canvas-grid: #3a2a10;
  --canvas-axis: #6a5540;
  --canvas-line: #ffd700;
  --scrollbar-track: #2d1b00;
  --scrollbar-thumb: #5a4530;
  --history-hover: #4a3520;
}

/* ========== Reset & Base ========== */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  min-height: 100vh;
  transition: background var(--transition-speed), color var(--transition-speed);
}

/* ========== App Container ========== */
.app-container {
  max-width: 900px;
  margin: 0 auto;
  padding: 16px;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* ========== Header ========== */
header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 12px 0;
  margin-bottom: 16px;
  flex-wrap: wrap;
  gap: 10px;
}

header h1 {
  font-size: 1.4rem;
  font-weight: 700;
  letter-spacing: 0.5px;
}

.header-controls {
  display: flex;
  gap: 8px;
  align-items: center;
}

.header-controls select,
.header-controls button {
  padding: 6px 14px;
  border: 1px solid var(--border-color);
  border-radius: 8px;
  background: var(--bg-btn);
  color: var(--text-primary);
  font-size: 0.85rem;
  cursor: pointer;
  transition: all var(--transition-speed);
}

.header-controls select:hover,
.header-controls button:hover {
  background: var(--bg-btn-hover);
}

/* ========== Main Layout ========== */
main {
  flex: 1;
  display: flex;
  gap: 16px;
  align-items: flex-start;
  flex-wrap: wrap;
}

.calculator-panel {
  flex: 1;
  min-width: 320px;
  background: var(--bg-secondary);
  border-radius: 16px;
  padding: 20px;
  box-shadow: 0 8px 32px var(--shadow-color);
  border: 1px solid var(--border-color);
}

/* ========== Display ========== */
.display {
  background: var(--bg-display);
  border-radius: 12px;
  padding: 16px 20px;
  margin-bottom: 16px;
  min-height: 90px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  align-items: flex-end;
  border: 1px solid var(--border-color);
  overflow: hidden;
}

.expression {
  font-size: 0.95rem;
  color: var(--text-secondary);
  word-break: break-all;
  text-align: right;
  width: 100%;
  min-height: 1.3em;
  transition: color var(--transition-speed);
}

.result {
  font-size: 2.2rem;
  font-weight: 700;
  color: var(--text-result);
  word-break: break-all;
  text-align: right;
  width: 100%;
  line-height: 1.2;
  transition: color var(--transition-speed);
}

/* ========== Buttons Grid ========== */
.buttons {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 8px;
}

.buttons button {
  padding: 14px 6px;
  border: 1px solid var(--border-color);
  border-radius: 10px;
  background: var(--bg-btn);
  color: var(--text-btn);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition-speed);
  user-select: none;
  -webkit-tap-highlight-color: transparent;
}

.buttons button:hover {
  background: var(--bg-btn-hover);
  transform: translateY(-1px);
  box-shadow: 0 4px 12px var(--shadow-color);
}

.buttons button:active {
  background: var(--bg-btn-active);
  transform: translateY(0);
  box-shadow: none;
}

.buttons button.btn-operator {
  background: var(--bg-btn-operator);
  color: #fff;
  border-color: transparent;
}

.buttons button.btn-operator:hover {
  background: var(--bg-btn-operator-hover);
}

.buttons button.btn-equals {
  background: var(--bg-btn-equals);
  color: #000;
  border-color: transparent;
  font-size: 1.3rem;
  grid-column: span 2;
}

.buttons button.btn-equals:hover {
  background: var(--bg-btn-equals-hover);
}

.buttons button.btn-danger {
  background: var(--bg-btn-danger);
  color: #fff;
  border-color: transparent;
}

.buttons button.btn-warning {
  background: var(--bg-btn-warning);
  color: #fff;
  border-color: transparent;
}

.buttons button.btn-zero {
  grid-column: span 2;
}

/* ========== Keyboard Hint ========== */
.keyboard-hint {
  text-align: center;
  font-size: 0.75rem;
  color: var(--text-secondary);
  margin-top: 12px;
  padding: 6px;
}

/* ========== History Panel ========== */
.history-panel {
  width: 280px;
  background: var(--bg-secondary);
  border-radius: 16px;
  padding: 16px;
  box-shadow: 0 8px 32px var(--shadow-color);
  border: 1px solid var(--border-color);
  max-height: 600px;
  display: flex;
  flex-direction: column;
  transition: opacity var(--transition-speed), transform var(--transition-speed);
}

.history-panel.hidden {
  display: none;
}

.panel-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 12px;
}

.panel-header h2 {
  font-size: 1rem;
  font-weight: 700;
}

.panel-header button {
  padding: 4px 12px;
  border: 1px solid var(--border-color);
  border-radius: 6px;
  background: var(--bg-btn);
  color: var(--text-primary);
  font-size: 0.8rem;
  cursor: pointer;
  transition: all var(--transition-speed);
}

.panel-header button:hover {
  background: var(--bg-btn-hover);
}

.history-list {
  flex: 1;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.history-list::-webkit-scrollbar {
  width: 6px;
}

.history-list::-webkit-scrollbar-track {
  background: var(--scrollbar-track);
  border-radius: 3px;
}

.history-list::-webkit-scrollbar-thumb {
  background: var(--scrollbar-thumb);
  border-radius: 3px;
}

.history-item {
  padding: 10px 12px;
  border-radius: 8px;
  background: var(--bg-display);
  border: 1px solid var(--border-color);
  cursor: pointer;
  transition: all var(--transition-speed);
}

.history-item:hover {
  background: var(--history-hover);
  border-color: var(--text-secondary);
}

.history-expr {
  font-size: 0.8rem;
  color: var(--text-secondary);
  word-break: break-all;
}

.history-result {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--text-result);
  word-break: break-all;
}

/* ========== Graph Panel ========== */
.graph-panel {
  width: 100%;
  background: var(--bg-secondary);
  border-radius: 16px;
  padding: 16px;
  box-shadow: 0 8px 32px var(--shadow-color);
  border: 1px solid var(--border-color);
  margin-top: 16px;
  transition: opacity var(--transition-speed), transform var(--transition-speed);
}

.graph-panel.hidden {
  display: none;
}

.graph-controls {
  display: flex;
  gap: 8px;
  margin-bottom: 12px;
  flex-wrap: wrap;
}

.graph-controls input {
  flex: 1;
  min-width: 200px;
  padding: 8px 14px;
  border: 1px solid var(--border-color);
  border-radius: 8px;
  background: var(--bg-display);
  color: var(--text-primary);
  font-size: 0.95rem;
  outline: none;
  transition: border-color var(--transition-speed);
}

.graph-controls input:focus {
  border-color: var(--text-result);
}

.graph-controls button {
  padding: 8px 18px;
  border: 1px solid var(--border-color);
  border-radius: 8px;
  background: var(--bg-btn);
  color: var(--text-primary);
  font-size: 0.9rem;
  cursor: pointer;
  transition: all var(--transition-speed);
}

.graph-controls button:hover {
  background: var(--bg-btn-hover);
}

.canvas-container {
  position: relative;
  width: 100%;
  border-radius: 12px;
  overflow: hidden;
  border: 1px solid var(--border-color);
}

#graph-canvas {
  width: 100%;
  height: 400px;
  display: block;
  background: var(--canvas-bg);
}

.graph-coords {
  position: absolute;
  bottom: 8px;
  right: 12px;
  font-size: 0.8rem;
  color: var(--text-secondary);
  background: rgba(0, 0, 0, 0.5);
  padding: 2px 8px;
  border-radius: 4px;
  pointer-events: none;
}

.graph-range {
  display: flex;
  gap: 16px;
  margin-top: 12px;
  flex-wrap: wrap;
  align-items: center;
}

.graph-range label {
  font-size: 0.85rem;
  color: var(--text-secondary);
  display: flex;
  align-items: center;
  gap: 4px;
}

.graph-range input {
  width: 70px;
  padding: 4px 8px;
  border: 1px solid var(--border-color);
  border-radius: 6px;
  background: var(--bg-display);
  color: var(--text-primary);
  font-size: 0.85rem;
  text-align: center;
}

/* ========== Responsive ========== */
@media (max-width: 700px) {
  .app-container {
    padding: 8px;
  }

  header h1 {
    font-size: 1.1rem;
  }

  .calculator-panel {
    min-width: 0;
    padding: 12px;
  }

  .buttons button {
    padding: 12px 4px;
    font-size: 0.85rem;
  }

  .result {
    font-size: 1.6rem;
  }

  .history-panel {
    width: 100%;
    max-height: 300px;
  }

  #graph-canvas {
    height: 280px;
  }
}

@media (max-width: 400px) {
  .buttons {
    gap: 5px;
  }

  .buttons button {
    padding: 10px 2px;
    font-size: 0.8rem;
    border-radius: 8px;
  }

  .result {
    font-size: 1.3rem;
  }
}

/* ========== Animations ========== */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(-8px); }
  to { opacity: 1; transform: translateY(0); }
}

.history-item {
  animation: fadeIn 0.2s ease;
}

/* ========== Error state ========== */
.result.error {
  color: var(--bg-btn-danger);
  font-size: 1.2rem;
}