:root {
  --bg-dark: #0f172a;
  --bg-card: rgba(30, 41, 59, 0.7);
  --bg-card-hover: rgba(30, 41, 59, 0.9);
  --border-color: rgba(255, 255, 255, 0.1);
  --text-main: #f8fafc;
  --text-muted: #94a3b8;
  --accent-cyan: #38bdf8;
  --accent-purple: #c084fc;
  --accent-pink: #f472b6;
  --accent-green: #4ade80;
  --code-bg: #090d16;
  --font-main: 'Outfit', -apple-system, BlinkMacSystemFont, sans-serif;
  --font-code: 'Fira Code', monospace;
}

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

body {
  background-color: var(--bg-dark);
  background-image: 
    radial-gradient(circle at 15% 15%, rgba(56, 189, 248, 0.12) 0%, transparent 40%),
    radial-gradient(circle at 85% 85%, rgba(192, 132, 252, 0.12) 0%, transparent 40%);
  background-attachment: fixed;
  color: var(--text-main);
  font-family: var(--font-main);
  line-height: 1.6;
  min-height: 100vh;
}

.app-container {
  max-width: 1280px;
  margin: 0 auto;
  padding: 2rem 1.5rem;
}

/* Header */
.hero-header {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
  margin-bottom: 2rem;
  padding-bottom: 1.5rem;
  border-bottom: 1px solid var(--border-color);
}

.logo-area {
  display: flex;
  align-items: center;
  gap: 1.25rem;
}

.lambda-symbol {
  font-size: 3.5rem;
  font-weight: 800;
  color: var(--accent-cyan);
  background: linear-gradient(135deg, var(--accent-cyan), var(--accent-purple));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  line-height: 1;
  text-shadow: 0 0 30px rgba(56, 189, 248, 0.3);
}

.hero-header h1 {
  font-size: 2.25rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.subtitle {
  color: var(--text-muted);
  font-size: 1.05rem;
}

/* Navigation Tabs */
.nav-tabs {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
}

.tab-btn {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  color: var(--text-muted);
  padding: 0.65rem 1.25rem;
  border-radius: 10px;
  font-family: var(--font-main);
  font-size: 0.95rem;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.2s ease;
  backdrop-filter: blur(8px);
}

.tab-btn:hover {
  background: var(--bg-card-hover);
  color: var(--text-main);
  border-color: var(--accent-cyan);
}

.tab-btn.active {
  background: linear-gradient(135deg, rgba(56, 189, 248, 0.2), rgba(192, 132, 252, 0.2));
  color: var(--accent-cyan);
  border-color: var(--accent-cyan);
  box-shadow: 0 4px 15px rgba(56, 189, 248, 0.15);
}

/* Content Panels */
.tab-content {
  display: none;
}

.tab-content.active {
  display: block;
  animation: fadeIn 0.3s ease;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(6px); }
  to { opacity: 1; transform: translateY(0); }
}

/* Cards & Layout */
.hero-card {
  background: linear-gradient(135deg, rgba(30, 41, 59, 0.8), rgba(15, 23, 42, 0.9));
  border: 1px solid rgba(56, 189, 248, 0.25);
  border-radius: 16px;
  padding: 2rem;
  margin-bottom: 1.75rem;
  box-shadow: 0 10px 30px rgba(0,0,0,0.3);
}

.hero-card h2 {
  font-size: 1.6rem;
  margin-bottom: 0.75rem;
  color: var(--accent-cyan);
}

.card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: 16px;
  padding: 1.75rem;
  margin-bottom: 1.5rem;
  backdrop-filter: blur(12px);
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.2);
}

.card h2, .card h3 {
  margin-bottom: 1rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.grid-2col {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(340px, 1fr));
  gap: 1.5rem;
  margin-bottom: 1.5rem;
}

.grid-3col {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 1.25rem;
}

/* Grammar Box & Rules */
.grammar-box {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  margin: 1rem 0;
}

.rule-item {
  background: var(--code-bg);
  padding: 0.9rem 1.1rem;
  border-radius: 10px;
  border-left: 3px solid var(--accent-cyan);
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
}

.rule-type {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--accent-purple);
  font-weight: 600;
}

.rule-expr {
  font-family: var(--font-code);
  font-size: 1.15rem;
  color: var(--accent-cyan);
  font-weight: 600;
}

.rule-desc {
  font-size: 0.9rem;
  color: var(--text-muted);
}

.rule-card {
  background: var(--code-bg);
  padding: 1rem;
  border-radius: 10px;
  margin-bottom: 0.75rem;
}

.rule-card h4 {
  color: var(--accent-pink);
  font-size: 0.95rem;
  margin-bottom: 0.35rem;
}

.rule-card code {
  font-family: var(--font-code);
  color: var(--accent-cyan);
  display: inline-block;
  margin-top: 0.5rem;
}

.callout {
  padding: 1rem;
  border-radius: 10px;
  font-size: 0.92rem;
  margin-top: 1rem;
}

.callout.note {
  background: rgba(56, 189, 248, 0.1);
  border: 1px solid rgba(56, 189, 248, 0.3);
}

.callout.tip {
  background: rgba(74, 222, 128, 0.1);
  border: 1px solid rgba(74, 222, 128, 0.3);
}

.strategy-card {
  background: var(--code-bg);
  padding: 1.25rem;
  border-radius: 12px;
}

.strategy-card h4 {
  color: var(--accent-purple);
  margin-bottom: 0.5rem;
}

.code-preview {
  margin-top: 0.75rem;
  font-family: var(--font-code);
  font-size: 0.85rem;
  color: var(--accent-cyan);
}

/* Evaluator Panel */
.evaluator-container {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.presets-toolbar {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  flex-wrap: wrap;
  margin: 1rem 0;
}

.presets-toolbar label {
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--text-muted);
}

.preset-btn {
  background: var(--code-bg);
  border: 1px solid var(--border-color);
  color: var(--text-main);
  padding: 0.4rem 0.8rem;
  border-radius: 6px;
  font-family: var(--font-code);
  font-size: 0.85rem;
  cursor: pointer;
  transition: all 0.2s ease;
}

.preset-btn:hover {
  border-color: var(--accent-cyan);
  color: var(--accent-cyan);
  background: rgba(56, 189, 248, 0.1);
}

.input-group {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.input-wrapper {
  display: flex;
  gap: 0.5rem;
}

#lambda-input {
  flex: 1;
  background: var(--code-bg);
  border: 1px solid var(--border-color);
  border-radius: 10px;
  padding: 0.85rem 1.1rem;
  color: var(--text-main);
  font-family: var(--font-code);
  font-size: 1.05rem;
  outline: none;
  transition: border-color 0.2s ease;
}

#lambda-input:focus {
  border-color: var(--accent-cyan);
  box-shadow: 0 0 12px rgba(56, 189, 248, 0.2);
}

.controls {
  display: flex;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
}

.controls label {
  font-size: 0.9rem;
  color: var(--text-muted);
}

#strategy-select {
  background: var(--code-bg);
  border: 1px solid var(--border-color);
  color: var(--text-main);
  padding: 0.6rem 1rem;
  border-radius: 8px;
  font-family: var(--font-main);
  outline: none;
  cursor: pointer;
}

.btn {
  padding: 0.65rem 1.25rem;
  border-radius: 8px;
  font-weight: 600;
  font-family: var(--font-main);
  cursor: pointer;
  border: none;
  transition: all 0.2s ease;
}

.btn.primary {
  background: linear-gradient(135deg, #0284c7, #7e22ce);
  color: #fff;
  box-shadow: 0 4px 14px rgba(2, 132, 199, 0.3);
}

.btn.primary:hover {
  transform: translateY(-1px);
  box-shadow: 0 6px 20px rgba(2, 132, 199, 0.4);
}

.btn.secondary {
  background: var(--code-bg);
  border: 1px solid var(--border-color);
  color: var(--accent-cyan);
  font-size: 1.2rem;
}

.btn.small {
  padding: 0.4rem 0.8rem;
  font-size: 0.85rem;
  background: var(--code-bg);
  border: 1px solid var(--border-color);
  color: var(--text-main);
}

.btn.small:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

.btn.success {
  background: rgba(74, 222, 128, 0.15);
  border: 1px solid rgba(74, 222, 128, 0.4);
  color: var(--accent-green);
}

/* Trace Step View */
.execution-results {
  background: var(--code-bg);
}

.results-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1rem;
  padding-bottom: 0.75rem;
  border-bottom: 1px solid var(--border-color);
  flex-wrap: wrap;
  gap: 1rem;
}

.stepper-controls {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

#step-indicator {
  font-family: var(--font-code);
  font-size: 0.85rem;
  color: var(--accent-cyan);
}

.step-display {
  background: var(--bg-dark);
  border: 1px solid rgba(56, 189, 248, 0.3);
  border-radius: 12px;
  padding: 1.5rem;
  min-height: 120px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  text-align: center;
  margin-bottom: 1.5rem;
}

.step-expr-large {
  font-family: var(--font-code);
  font-size: 1.4rem;
  color: var(--accent-cyan);
  font-weight: 600;
  word-break: break-all;
  margin-bottom: 0.5rem;
}

.step-action-desc {
  font-size: 0.9rem;
  color: var(--accent-purple);
  background: rgba(192, 132, 252, 0.1);
  padding: 0.35rem 0.85rem;
  border-radius: 20px;
}

.steps-list {
  max-height: 280px;
  overflow-y: auto;
  padding-left: 1.5rem;
}

.steps-list li {
  font-family: var(--font-code);
  font-size: 0.95rem;
  padding: 0.4rem 0;
  color: var(--text-muted);
  border-bottom: 1px dashed rgba(255,255,255,0.05);
}

.steps-list li.current-step {
  color: var(--accent-cyan);
  font-weight: 600;
}

/* Encoding Subtabs */
.encoding-tabs {
  display: flex;
  gap: 0.75rem;
  margin-bottom: 1.5rem;
}

.subtab-btn {
  background: var(--code-bg);
  border: 1px solid var(--border-color);
  color: var(--text-muted);
  padding: 0.5rem 1rem;
  border-radius: 8px;
  font-family: var(--font-main);
  cursor: pointer;
  transition: all 0.2s ease;
}

.subtab-btn.active {
  background: var(--accent-purple);
  color: #fff;
  border-color: var(--accent-purple);
}

.subtab-content {
  display: none;
}

.subtab-content.active {
  display: block;
}

.code-block {
  background: var(--code-bg);
  padding: 1.25rem;
  border-radius: 10px;
  font-family: var(--font-code);
  font-size: 0.95rem;
  color: var(--accent-cyan);
  line-height: 1.8;
}

.code-block .kw { color: var(--accent-pink); font-weight: 600; }
.code-block .cm { color: var(--text-muted); font-size: 0.85rem; }

.numeral-box {
  background: var(--code-bg);
  padding: 1.25rem;
  border-radius: 12px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.5rem;
  text-align: center;
}

.num-val {
  font-size: 1.8rem;
  font-weight: 700;
  color: var(--accent-purple);
}

.formula-banner {
  background: linear-gradient(135deg, rgba(192, 132, 252, 0.15), rgba(244, 114, 182, 0.15));
  border: 1px solid rgba(192, 132, 252, 0.4);
  padding: 1.25rem;
  border-radius: 12px;
  font-family: var(--font-code);
  font-size: 1.3rem;
  color: var(--accent-pink);
  text-align: center;
  margin: 1.25rem 0;
  font-weight: 700;
}

.code-comparison {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 1.25rem;
  margin-top: 1.25rem;
}

.code-column {
  background: var(--code-bg);
  padding: 1.25rem;
  border-radius: 12px;
}

.code-column h4 {
  color: var(--accent-cyan);
  margin-bottom: 0.75rem;
  font-size: 0.95rem;
}

.code-snippet {
  font-family: var(--font-code);
  font-size: 0.88rem;
  color: var(--text-main);
  white-space: pre-wrap;
}

/* Impact Section */
.impact-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1.5rem;
}

.impact-card {
  position: relative;
  overflow: hidden;
}

.impact-badge {
  position: absolute;
  top: 1rem;
  right: 1rem;
  background: rgba(56, 189, 248, 0.15);
  color: var(--accent-cyan);
  border: 1px solid rgba(56, 189, 248, 0.3);
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  padding: 0.2rem 0.6rem;
  border-radius: 20px;
}

.impact-card h3 {
  font-size: 1.15rem;
  color: var(--accent-purple);
  margin-bottom: 0.75rem;
  padding-right: 4rem;
}

.impact-card ul {
  padding-left: 1.2rem;
  margin-top: 0.75rem;
  font-size: 0.92rem;
  color: var(--text-muted);
}

.impact-card li {
  margin-bottom: 0.5rem;
}

.isomorphism-box {
  background: var(--code-bg);
  border-radius: 10px;
  padding: 1rem;
  margin: 1rem 0;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.iso-row {
  display: flex;
  justify-content: space-between;
  font-family: var(--font-code);
  font-size: 0.88rem;
  color: var(--accent-cyan);
}

.margin-top {
  margin-top: 1.5rem;
}

/* Table */
.table-responsive {
  overflow-x: auto;
}

.comparison-table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 1rem;
  font-size: 0.92rem;
}

.comparison-table th, .comparison-table td {
  padding: 0.85rem 1rem;
  text-align: left;
  border-bottom: 1px solid var(--border-color);
}

.comparison-table th {
  background: rgba(255,255,255,0.03);
  color: var(--accent-cyan);
  font-weight: 600;
}

.comparison-table td code {
  font-family: var(--font-code);
  color: var(--accent-pink);
}