:root {
  --bg-grad-1: #0f172a;
  --bg-grad-2: #1e293b;
  --panel: rgba(255, 255, 255, 0.06);
  --panel-strong: rgba(255, 255, 255, 0.10);
  --border: rgba(255, 255, 255, 0.10);
  --text: #f8fafc;
  --text-dim: #94a3b8;
  --accent: #6366f1;
  --accent-2: #8b5cf6;
  --danger: #ef4444;
  --operator: #f59e0b;
  --success: #10b981;
  --key-bg: rgba(255, 255, 255, 0.06);
  --key-bg-hover: rgba(255, 255, 255, 0.12);
  --key-shadow: 0 6px 18px rgba(0, 0, 0, 0.35);
  --display-bg: rgba(0, 0, 0, 0.28);
  --shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.6);
  --radius: 18px;
}

[data-theme="light"] {
  --bg-grad-1: #e0e7ff;
  --bg-grad-2: #fdf2f8;
  --panel: rgba(255, 255, 255, 0.65);
  --panel-strong: rgba(255, 255, 255, 0.85);
  --border: rgba(15, 23, 42, 0.08);
  --text: #0f172a;
  --text-dim: #475569;
  --key-bg: rgba(255, 255, 255, 0.9);
  --key-bg-hover: #ffffff;
  --display-bg: rgba(255, 255, 255, 0.85);
  --key-shadow: 0 6px 18px rgba(99, 102, 241, 0.15);
  --shadow: 0 25px 50px -12px rgba(99, 102, 241, 0.25);
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  min-height: 100vh;
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  color: var(--text);
  background: radial-gradient(at 20% 0%, var(--accent-2) 0%, transparent 40%),
              radial-gradient(at 90% 80%, var(--accent) 0%, transparent 40%),
              linear-gradient(135deg, var(--bg-grad-1), var(--bg-grad-2));
  background-attachment: fixed;
  transition: background 0.5s ease, color 0.3s ease;
}

.app {
  max-width: 1100px;
  margin: 0 auto;
  padding: 28px 20px 40px;
}

.app-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 22px;
}

.app-header h1 {
  font-size: 28px;
  letter-spacing: -0.02em;
  margin: 0;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

.app-header .dot {
  color: var(--operator);
  -webkit-text-fill-color: var(--operator);
}

.header-actions {
  display: flex;
  gap: 10px;
}

.icon-btn, .mode-btn {
  border: 1px solid var(--border);
  background: var(--panel);
  color: var(--text);
  padding: 9px 14px;
  border-radius: 12px;
  cursor: pointer;
  font-weight: 500;
  font-size: 14px;
  backdrop-filter: blur(12px);
  transition: transform 0.15s ease, background 0.2s ease;
}

.icon-btn:hover, .mode-btn:hover {
  background: var(--panel-strong);
  transform: translateY(-1px);
}

.icon-btn { font-size: 16px; line-height: 1; }

.calculator-wrap {
  display: grid;
  grid-template-columns: minmax(320px, 1fr) 320px;
  gap: 22px;
  align-items: start;
}

@media (max-width: 820px) {
  .calculator-wrap { grid-template-columns: 1fr; }
}

.calculator {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px;
  box-shadow: var(--shadow);
  backdrop-filter: blur(16px);
}

.display {
  background: var(--display-bg);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 18px 20px;
  min-height: 110px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  align-items: flex-end;
  margin-bottom: 18px;
  overflow: hidden;
}

.expression {
  color: var(--text-dim);
  font-size: 16px;
  font-family: 'JetBrains Mono', 'SF Mono', Menlo, monospace;
  min-height: 22px;
  word-break: break-all;
  text-align: right;
  width: 100%;
  opacity: 0.85;
}

.result {
  font-size: 44px;
  font-weight: 600;
  font-family: 'JetBrains Mono', 'SF Mono', Menlo, monospace;
  letter-spacing: -0.02em;
  margin-top: 4px;
  word-break: break-all;
  text-align: right;
  width: 100%;
  line-height: 1.1;
}

.result.error { color: var(--danger); font-size: 28px; }

.keys {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

.keys.scientific { grid-template-columns: repeat(5, 1fr); }

.key {
  border: 1px solid var(--border);
  background: var(--key-bg);
  color: var(--text);
  font-size: 19px;
  font-weight: 500;
  padding: 16px 8px;
  border-radius: 14px;
  cursor: pointer;
  box-shadow: var(--key-shadow);
  transition: transform 0.1s ease, background 0.2s ease, box-shadow 0.2s ease;
  user-select: none;
  font-family: 'JetBrains Mono', 'SF Mono', Menlo, monospace;
}

.key:hover { background: var(--key-bg-hover); transform: translateY(-2px); }
.key:active { transform: translateY(0); box-shadow: 0 2px 6px rgba(0,0,0,0.3); }

.key.op { color: var(--operator); }
.key.op-eq {
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: white;
  border: none;
  box-shadow: 0 6px 22px rgba(99, 102, 241, 0.45);
}
.key.op-eq:hover { filter: brightness(1.1); }

.key.fn { color: var(--accent); font-size: 16px; }
.key.danger { color: var(--danger); }
.key.wide { grid-column: span 2; }

.history-panel {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  box-shadow: var(--shadow);
  backdrop-filter: blur(16px);
  max-height: 600px;
  display: flex;
  flex-direction: column;
}

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

.history-header h2 {
  font-size: 16px;
  margin: 0;
  font-weight: 600;
}

.link-btn {
  background: none;
  border: none;
  color: var(--accent);
  cursor: pointer;
  font-size: 13px;
  padding: 4px 8px;
  border-radius: 8px;
}
.link-btn:hover { background: var(--panel-strong); }

.history-list {
  list-style: none;
  margin: 0;
  padding: 0;
  overflow-y: auto;
  flex: 1;
}

.history-item {
  padding: 10px 12px;
  border-radius: 10px;
  cursor: pointer;
  margin-bottom: 6px;
  border: 1px solid transparent;
  transition: background 0.2s ease, border-color 0.2s ease;
}

.history-item:hover {
  background: var(--panel-strong);
  border-color: var(--border);
}

.history-item .expr {
  font-family: 'JetBrains Mono', 'SF Mono', Menlo, monospace;
  font-size: 13px;
  color: var(--text-dim);
  word-break: break-all;
}

.history-item .res {
  font-family: 'JetBrains Mono', 'SF Mono', Menlo, monospace;
  font-size: 17px;
  font-weight: 600;
  margin-top: 3px;
  word-break: break-all;
}

.history-empty {
  color: var(--text-dim);
  font-size: 13px;
  text-align: center;
  padding: 24px 8px;
}
.history-empty code {
  background: var(--panel-strong);
  padding: 2px 6px;
  border-radius: 5px;
  font-size: 12px;
}

.app-footer {
  margin-top: 22px;
  text-align: center;
  color: var(--text-dim);
  font-size: 13px;
}

kbd {
  background: var(--panel-strong);
  border: 1px solid var(--border);
  border-radius: 5px;
  padding: 1px 6px;
  font-family: 'JetBrains Mono', monospace;
  font-size: 12px;
}

@keyframes pop {
  0% { transform: scale(1); }
  50% { transform: scale(1.04); }
  100% { transform: scale(1); }
}
.result.pop { animation: pop 0.18s ease; }