:root {
  --font-body: 'Inter', system-ui, sans-serif;
  --font-mono: 'JetBrains Mono', monospace;
  --bg: #0a0a0f;
  --bg-card: #12121a;
  --bg-display: #0d0d14;
  --border: #1e1e2e;
  --text: #e4e4ef;
  --text-muted: #8888a0;
  --accent: #6c5ce7;
  --accent-hover: #7c6df7;
  --operator: #2d2d3f;
  --operator-hover: #3d3d5f;
  --number: #1a1a28;
  --number-hover: #24243a;
  --equals: #6c5ce7;
  --equals-hover: #7c6df7;
  --clear: #e74c3c;
  --clear-hover: #ff5c4c;
  --radius: 12px;
  --radius-sm: 8px;
}

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

body {
  font-family: var(--font-body);
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* Header */
.header {
  border-bottom: 1px solid var(--border);
  padding: 0 24px;
}
.header-inner {
  max-width: 1100px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 60px;
}
.logo {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  color: var(--text);
  font-weight: 600;
  font-size: 1.1rem;
}
.logo-icon { font-size: 1.4rem; }
.nav { display: flex; gap: 20px; }
.nav-link {
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.9rem;
  transition: color 0.2s;
}
.nav-link:hover { color: var(--accent); }

/* Main */
.main {
  flex: 1;
  max-width: 1100px;
  margin: 0 auto;
  padding: 40px 24px;
  width: 100%;
}

.hero {
  text-align: center;
  margin-bottom: 40px;
}
.hero h1 {
  font-family: var(--font-mono);
  font-size: 2.2rem;
  font-weight: 700;
  margin-bottom: 8px;
}
.subtitle {
  color: var(--text-muted);
  font-size: 1.05rem;
}
.subtitle strong { color: var(--clear); }

/* Calculator Layout */
.calculator-container {
  display: grid;
  grid-template-columns: 340px 280px;
  gap: 24px;
  justify-content: center;
  margin-bottom: 48px;
}

/* Calculator */
.calculator {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  box-shadow: 0 8px 32px rgba(0,0,0,0.3);
}

.display {
  background: var(--bg-display);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 20px;
  margin-bottom: 16px;
  min-height: 90px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  align-items: flex-end;
  overflow: hidden;
}
.display-expression {
  font-family: var(--font-mono);
  font-size: 0.9rem;
  color: var(--text-muted);
  min-height: 1.2em;
  word-break: break-all;
}
.display-result {
  font-family: var(--font-mono);
  font-size: 2rem;
  font-weight: 500;
  color: var(--text);
  word-break: break-all;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
}

.btn {
  font-family: var(--font-mono);
  font-size: 1.2rem;
  font-weight: 500;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 16px;
  cursor: pointer;
  transition: all 0.15s;
  outline: none;
}
.btn:active { transform: scale(0.95); }

.btn-number {
  background: var(--number);
  color: var(--text);
}
.btn-number:hover { background: var(--number-hover); }

.btn-operator {
  background: var(--operator);
  color: var(--accent);
}
.btn-operator:hover { background: var(--operator-hover); }

.btn-clear {
  background: rgba(231, 76, 60, 0.15);
  color: var(--clear);
  border-color: rgba(231, 76, 60, 0.3);
}
.btn-clear:hover { background: rgba(231, 76, 60, 0.25); }

.btn-equals {
  background: var(--equals);
  color: #fff;
  border-color: var(--equals);
}
.btn-equals:hover { background: var(--equals-hover); }

/* History Panel */
.history-panel {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  max-height: 500px;
  display: flex;
  flex-direction: column;
}
.history-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 16px;
}
.history-header h3 {
  font-family: var(--font-mono);
  font-size: 1rem;
  font-weight: 600;
}
.history-clear {
  background: none;
  border: 1px solid var(--border);
  color: var(--text-muted);
  font-size: 0.8rem;
  padding: 4px 12px;
  border-radius: 6px;
  cursor: pointer;
  transition: all 0.2s;
}
.history-clear:hover {
  border-color: var(--clear);
  color: var(--clear);
}

.history-list {
  flex: 1;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  gap: 8px;
}
.history-empty {
  color: var(--text-muted);
  font-size: 0.9rem;
  text-align: center;
  padding: 20px;
}
.history-item {
  background: var(--bg-display);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 10px 14px;
  cursor: pointer;
  transition: border-color 0.2s;
}
.history-item:hover { border-color: var(--accent); }
.history-item .expr {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--text-muted);
}
.history-item .res {
  font-family: var(--font-mono);
  font-size: 1.1rem;
  color: var(--text);
  font-weight: 500;
}

/* Info Cards */
.info-cards {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 20px;
}
.info-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
}
.info-card h3 {
  font-size: 1rem;
  margin-bottom: 8px;
}
.info-card p {
  color: var(--text-muted);
  font-size: 0.9rem;
  line-height: 1.5;
}

/* Footer */
.footer {
  border-top: 1px solid var(--border);
  padding: 20px 24px;
  text-align: center;
}
.footer p {
  color: var(--text-muted);
  font-size: 0.85rem;
}
.footer a {
  color: var(--accent);
  text-decoration: none;
}
.footer a:hover { text-decoration: underline; }

/* Responsive */
@media (max-width: 768px) {
  .calculator-container {
    grid-template-columns: 1fr;
    max-width: 360px;
    margin-left: auto;
    margin-right: auto;
  }
  .info-cards {
    grid-template-columns: 1fr;
  }
  .hero h1 { font-size: 1.6rem; }
  .nav { display: none; }
}