/* ===== Design System — 计算工坊 v2 ===== */

:root {
  color-scheme: light;
  --bg: #f8f9fc;
  --bg-alt: #ffffff;
  --surface: #ffffff;
  --surface-hover: #f1f3f9;
  --border: #e2e6ef;
  --border-focus: #6366f1;
  --accent: #6366f1;
  --accent-hover: #4f46e5;
  --accent-light: rgba(99, 102, 241, 0.08);
  --accent-mid: rgba(99, 102, 241, 0.15);
  --green: #10b981;
  --green-light: rgba(16, 185, 129, 0.1);
  --red: #ef4444;
  --red-light: rgba(239, 68, 68, 0.08);
  --orange: #f59e0b;
  --orange-light: rgba(245, 158, 11, 0.1);
  --text: #1e1e2e;
  --text-secondary: #64748b;
  --text-tertiary: #94a3b8;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.04);
  --shadow: 0 1px 3px rgba(0, 0, 0, 0.06), 0 1px 2px rgba(0, 0, 0, 0.04);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.06), 0 1px 3px rgba(0, 0, 0, 0.04);
  --shadow-lg: 0 10px 30px rgba(0, 0, 0, 0.08);
  --radius: 12px;
  --radius-sm: 8px;
  --radius-lg: 16px;
  --sans: "Inter", "Noto Sans SC", "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
  --mono: "JetBrains Mono", "SF Mono", "Cascadia Code", "Fira Code", Consolas, monospace;
  --transition: 0.15s ease;
}

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

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
}

body {
  font-family: var(--sans);
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

img {
  max-width: 100%;
  display: block;
}

a {
  color: inherit;
  text-decoration: none;
}

button {
  cursor: pointer;
  font-family: inherit;
}

/* ===== Layout ===== */
.wrap {
  width: min(1120px, 100% - 2rem);
  margin-inline: auto;
}

/* ===== Header / Topbar ===== */
.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 1rem 0;
  border-bottom: 1px solid var(--border);
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.625rem;
  text-decoration: none;
  flex-shrink: 0;
}

.brand-icon {
  width: 36px;
  height: 36px;
  border-radius: 10px;
  background: var(--accent);
  color: #fff;
  display: grid;
  place-items: center;
  font-weight: 700;
  font-size: 0.8rem;
  font-family: var(--mono);
  letter-spacing: -0.02em;
}

.brand-name {
  font-weight: 650;
  font-size: 1.05rem;
  letter-spacing: -0.01em;
}

/* ===== Navigation ===== */
.nav {
  display: flex;
  align-items: center;
  gap: 0.25rem;
}

.nav-link {
  padding: 0.375rem 0.75rem;
  border-radius: var(--radius-sm);
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--text-secondary);
  transition: color var(--transition), background var(--transition);
  white-space: nowrap;
}

.nav-link:hover {
  color: var(--text);
  background: var(--surface-hover);
}

.nav-link.active {
  color: var(--accent);
  background: var(--accent-light);
}

/* ===== Mobile Menu Toggle ===== */
.menu-toggle {
  display: none;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--surface);
  color: var(--text);
  font-size: 1.25rem;
  transition: background var(--transition);
}

.menu-toggle:hover {
  background: var(--surface-hover);
}

/* ===== Hero (index only) ===== */
.hero {
  padding: 4rem 0 3rem;
  text-align: center;
  max-width: 640px;
  margin-inline: auto;
}

.hero h1 {
  font-size: clamp(1.75rem, 4vw, 2.5rem);
  font-weight: 750;
  letter-spacing: -0.025em;
  line-height: 1.2;
  margin-bottom: 0.75rem;
}

.hero p {
  color: var(--text-secondary);
  font-size: 1.05rem;
  line-height: 1.7;
  margin-bottom: 1.5rem;
}

.hero-actions {
  display: flex;
  gap: 0.75rem;
  justify-content: center;
  flex-wrap: wrap;
}

/* ===== Module Grid (index) ===== */
.modules {
  padding-bottom: 4rem;
}

.modules-title {
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-tertiary);
  margin-bottom: 1rem;
}

.modules-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 0.75rem;
}

.module-card {
  display: flex;
  flex-direction: column;
  gap: 0.375rem;
  padding: 1.25rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  transition: border-color var(--transition), box-shadow var(--transition);
}

.module-card:hover {
  border-color: var(--accent);
  box-shadow: var(--shadow-md), 0 0 0 3px var(--accent-light);
}

.module-card h3 {
  font-size: 0.95rem;
  font-weight: 600;
}

.module-card p {
  font-size: 0.85rem;
  color: var(--text-secondary);
  line-height: 1.5;
}

.module-card .card-tag {
  display: inline-flex;
  align-items: center;
  gap: 0.25rem;
  font-size: 0.7rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--accent);
  margin-bottom: 0.25rem;
}

/* ===== Page Content ===== */
.page {
  padding: 1.5rem 0 3rem;
}

.page-header {
  margin-bottom: 1.5rem;
}

.page-header h1 {
  font-size: 1.5rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.page-header p {
  color: var(--text-secondary);
  font-size: 0.9rem;
  margin-top: 0.25rem;
}

/* ===== Panel / Card ===== */
.panel {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
}

.panel + .panel {
  margin-top: 0.75rem;
}

.panel-title {
  font-size: 1rem;
  font-weight: 600;
  margin-bottom: 1rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.panel-title .tag {
  font-size: 0.65rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  padding: 0.2rem 0.5rem;
  border-radius: 999px;
  background: var(--accent-light);
  color: var(--accent);
}

/* ===== Grid Layouts ===== */
.grid-2 {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 0.75rem;
}

.grid-3 {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.75rem;
}

.stack {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

/* ===== Form Elements ===== */
.field {
  display: flex;
  flex-direction: column;
  gap: 0.375rem;
  margin-bottom: 1rem;
}

.field:last-child {
  margin-bottom: 0;
}

.field label {
  font-size: 0.8rem;
  font-weight: 550;
  color: var(--text-secondary);
}

input[type="text"],
input[type="number"],
textarea,
select {
  width: 100%;
  padding: 0.5rem 0.75rem;
  background: var(--bg);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  font-family: var(--mono);
  font-size: 0.875rem;
  line-height: 1.5;
  outline: none;
  transition: border-color var(--transition), box-shadow var(--transition);
}

input:focus,
textarea:focus,
select:focus {
  border-color: var(--border-focus);
  box-shadow: 0 0 0 3px var(--accent-light);
}

textarea {
  min-height: 100px;
  resize: vertical;
}

input::placeholder,
textarea::placeholder {
  color: var(--text-tertiary);
}

/* ===== Buttons ===== */
.actions {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
  margin-top: 1rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.375rem;
  padding: 0.5rem 1rem;
  border-radius: var(--radius-sm);
  font-weight: 600;
  font-size: 0.85rem;
  border: 1px solid transparent;
  transition: all var(--transition);
  line-height: 1.5;
  white-space: nowrap;
}

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

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

.btn-secondary {
  background: var(--surface);
  color: var(--text);
  border-color: var(--border);
}

.btn-secondary:hover {
  background: var(--surface-hover);
}

.btn-ghost {
  background: transparent;
  color: var(--text-secondary);
  border-color: transparent;
}

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

.btn-sm {
  padding: 0.375rem 0.625rem;
  font-size: 0.8rem;
}

/* ===== Result Display ===== */
.result-box {
  margin-top: 1rem;
  padding: 0.875rem 1rem;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  font-family: var(--mono);
  font-size: 0.9rem;
  line-height: 1.6;
  min-height: 2.75rem;
  word-break: break-all;
}

.result-box.success {
  background: var(--green-light);
  border-color: var(--green);
  color: #065f46;
}

.result-box.error {
  background: var(--red-light);
  border-color: var(--red);
  color: #991b1b;
}

.result-label {
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--text-tertiary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.25rem;
}

/* ===== Result Grid (for stats etc.) ===== */
.result-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
  gap: 0.5rem;
  margin-top: 1rem;
}

.result-item {
  padding: 0.75rem;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
}

.result-item .label {
  font-size: 0.7rem;
  font-weight: 600;
  color: var(--text-tertiary);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.result-item .value {
  font-family: var(--mono);
  font-size: 1rem;
  font-weight: 600;
  margin-top: 0.125rem;
}

/* ===== History List ===== */
.history {
  margin-top: 1rem;
}

.history-title {
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--text-tertiary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.5rem;
}

.history-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
  max-height: 200px;
  overflow-y: auto;
}

.history-item {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.375rem 0.625rem;
  border-radius: var(--radius-sm);
  font-family: var(--mono);
  font-size: 0.8rem;
  cursor: pointer;
  transition: background var(--transition);
}

.history-item:hover {
  background: var(--accent-light);
}

.history-item .expr {
  color: var(--text-secondary);
}

.history-item .val {
  font-weight: 600;
  color: var(--accent);
}

/* ===== Plot Area ===== */
.plot-canvas {
  width: 100%;
  height: 380px;
  margin-top: 1rem;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  overflow: hidden;
  background: var(--bg);
}

/* ===== LaTeX Preview ===== */
.latex-preview {
  margin-top: 1rem;
  padding: 1.5rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  min-height: 120px;
  font-size: 1.1rem;
  line-height: 2;
  overflow-x: auto;
}

/* ===== Footer ===== */
.footer {
  border-top: 1px solid var(--border);
  padding: 1.25rem 0;
  margin-top: auto;
}

.footer-inner {
  display: flex;
  gap: 1rem;
  align-items: center;
  flex-wrap: wrap;
  font-size: 0.8rem;
  color: var(--text-tertiary);
}

.footer-inner a {
  color: var(--text-tertiary);
  transition: color var(--transition);
}

.footer-inner a:hover {
  color: var(--text-secondary);
}

.footer-inner .record {
  display: inline-flex;
  align-items: center;
  gap: 0.375rem;
}

.footer-inner .record img {
  width: 16px;
  height: 16px;
}

/* ===== Utility ===== */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.text-mono {
  font-family: var(--mono);
}

.text-muted {
  color: var(--text-secondary);
}

.text-sm {
  font-size: 0.85rem;
}

.mt-1 { margin-top: 0.5rem; }
.mt-2 { margin-top: 1rem; }
.mb-1 { margin-bottom: 0.5rem; }
.mb-2 { margin-bottom: 1rem; }

/* ===== Responsive ===== */
@media (max-width: 768px) {
  .menu-toggle {
    display: flex;
  }

  .nav {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 0.5rem;
    flex-direction: column;
    box-shadow: var(--shadow-lg);
    z-index: 100;
  }

  .nav.open {
    display: flex;
  }

  .topbar {
    position: relative;
  }

  .nav-link {
    padding: 0.625rem 0.75rem;
  }

  .grid-2,
  .grid-3 {
    grid-template-columns: 1fr;
  }

  .hero {
    padding: 2.5rem 0 2rem;
  }

  .hero h1 {
    font-size: 1.5rem;
  }

  .result-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 480px) {
  .result-grid {
    grid-template-columns: 1fr;
  }

  .panel {
    padding: 1rem;
  }
}