/* public/css/main.css - ChatGPT-inspired Minimalist Light Design System */

:root {
  --bg-main: #ffffff;
  --bg-subtle: #f9fafb;
  --bg-muted: #f3f4f6;
  --bg-card: #ffffff;
  --border-subtle: #e5e7eb;
  --border-hover: #d1d5db;
  --border-focus: #9ca3af;
  
  --text-primary: #111827;
  --text-secondary: #4b5563;
  --text-muted: #6b7280;
  --text-light: #9ca3af;

  --accent-blue: #2563eb;
  --accent-blue-bg: #eff6ff;
  --accent-blue-border: #bfdbfe;

  --badge-beginner-bg: #ecfdf5;
  --badge-beginner-text: #059669;
  --badge-beginner-border: #a7f3d0;

  --badge-easy-bg: #eff6ff;
  --badge-easy-text: #2563eb;
  --badge-easy-border: #bfdbfe;

  --badge-intermediate-bg: #fffbeb;
  --badge-intermediate-text: #d97706;
  --badge-intermediate-border: #fde68a;

  --badge-advanced-bg: #faf5ff;
  --badge-advanced-text: #7e22ce;
  --badge-advanced-border: #e9d5ff;

  --badge-expert-bg: #fff1f2;
  --badge-expert-text: #e11d48;
  --badge-expert-border: #fecdd3;

  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 14px;
  --radius-xl: 18px;

  --shadow-subtle: 0 1px 3px rgba(0, 0, 0, 0.04), 0 1px 2px rgba(0, 0, 0, 0.02);
  --shadow-card: 0 4px 6px -1px rgba(0, 0, 0, 0.04), 0 2px 4px -1px rgba(0, 0, 0, 0.02);
  --shadow-float: 0 10px 15px -3px rgba(0, 0, 0, 0.06), 0 4px 6px -2px rgba(0, 0, 0, 0.03);

  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
}

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

body {
  font-family: var(--font-sans);
  background-color: var(--bg-main);
  color: var(--text-primary);
  line-height: 1.55;
  font-size: 15px;
  -webkit-font-smoothing: antialiased;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* Container */
.container {
  max-width: 1140px;
  margin: 0 auto;
  padding: 0 24px;
  width: 100%;
}

.container-narrow {
  max-width: 860px;
  margin: 0 auto;
  padding: 0 24px;
  width: 100%;
}

/* Global Top Navigation */
.platform-header {
  border-bottom: 1px solid var(--border-subtle);
  background-color: rgba(255, 255, 255, 0.96);
  backdrop-filter: blur(8px);
  position: sticky;
  top: 0;
  z-index: 100;
}

.nav-wrapper {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

.brand-link {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  color: var(--text-primary);
  font-weight: 600;
  font-size: 17px;
  letter-spacing: -0.01em;
}

.brand-logo-icon {
  width: 28px;
  height: 28px;
  border-radius: var(--radius-sm);
  background-color: var(--text-primary);
  color: #ffffff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 14px;
}

.brand-badge {
  font-size: 11px;
  font-weight: 500;
  background-color: var(--bg-muted);
  color: var(--text-secondary);
  padding: 2px 8px;
  border-radius: 999px;
  border: 1px solid var(--border-subtle);
}

.main-nav-links {
  display: flex;
  align-items: center;
  gap: 8px;
}

.nav-item {
  text-decoration: none;
  color: var(--text-secondary);
  font-size: 14px;
  font-weight: 500;
  padding: 8px 14px;
  border-radius: var(--radius-md);
  transition: all 0.15s ease;
}

.nav-item:hover {
  color: var(--text-primary);
  background-color: var(--bg-muted);
}

.nav-item.active {
  color: var(--text-primary);
  background-color: var(--bg-subtle);
  border: 1px solid var(--border-subtle);
}

.nav-actions {
  display: flex;
  align-items: center;
  gap: 12px;
}

.progress-pill {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background-color: var(--bg-subtle);
  border: 1px solid var(--border-subtle);
  padding: 5px 12px;
  border-radius: 999px;
  font-size: 12px;
  font-weight: 500;
  color: var(--text-secondary);
}

.progress-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background-color: #10b981;
}

/* Hero Section */
.hero-section {
  padding: 64px 0 48px;
  text-align: center;
}

.hero-tagline {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 13px;
  font-weight: 500;
  color: var(--text-secondary);
  background-color: var(--bg-subtle);
  border: 1px solid var(--border-subtle);
  padding: 4px 12px;
  border-radius: 999px;
  margin-bottom: 20px;
}

.hero-title {
  font-size: 40px;
  font-weight: 700;
  letter-spacing: -0.03em;
  color: var(--text-primary);
  margin-bottom: 14px;
  line-height: 1.15;
}

.hero-subtitle {
  font-size: 17px;
  color: var(--text-secondary);
  max-width: 620px;
  margin: 0 auto 36px;
  line-height: 1.5;
}

/* Category Grid (Homepage) */
.category-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
  margin-bottom: 56px;
}

.category-card {
  background-color: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-xl);
  padding: 32px 28px;
  display: flex;
  flex-direction: column;
  text-decoration: none;
  color: inherit;
  transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
  position: relative;
  box-shadow: var(--shadow-subtle);
}

.category-card:hover {
  transform: translateY(-2px);
  border-color: var(--border-hover);
  box-shadow: var(--shadow-float);
}

.cat-icon-wrap {
  width: 44px;
  height: 44px;
  border-radius: var(--radius-md);
  background-color: var(--bg-subtle);
  border: 1px solid var(--border-subtle);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  margin-bottom: 20px;
  color: var(--text-primary);
}

.cat-title {
  font-size: 20px;
  font-weight: 600;
  letter-spacing: -0.01em;
  color: var(--text-primary);
  margin-bottom: 8px;
}

.cat-desc {
  font-size: 14px;
  color: var(--text-secondary);
  line-height: 1.5;
  margin-bottom: 24px;
  flex-grow: 1;
}

.cat-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-top: 1px solid var(--border-subtle);
  padding-top: 16px;
  font-size: 13px;
  color: var(--text-muted);
}

.cat-count {
  font-weight: 500;
}

.cat-action {
  font-weight: 500;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 4px;
}

/* Category Detail Header */
.category-header {
  padding: 40px 0 28px;
  border-bottom: 1px solid var(--border-subtle);
  margin-bottom: 36px;
}

.category-breadcrumb {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
  color: var(--text-muted);
  margin-bottom: 12px;
}

.category-breadcrumb a {
  color: var(--text-secondary);
  text-decoration: none;
}

.category-breadcrumb a:hover {
  color: var(--text-primary);
}

.cat-page-title {
  font-size: 32px;
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--text-primary);
  margin-bottom: 8px;
}

.cat-page-desc {
  font-size: 15px;
  color: var(--text-secondary);
  max-width: 720px;
}

/* Lab Cards List */
.labs-list {
  display: flex;
  flex-direction: column;
  gap: 14px;
  margin-bottom: 64px;
}

.lab-row-card {
  background-color: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 20px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  text-decoration: none;
  color: inherit;
  transition: all 0.15s ease;
  box-shadow: var(--shadow-subtle);
  gap: 20px;
}

.lab-row-card:hover {
  border-color: var(--border-hover);
  background-color: var(--bg-subtle);
  box-shadow: var(--shadow-card);
}

.lab-row-left {
  display: flex;
  align-items: center;
  gap: 18px;
  flex-grow: 1;
}

.lab-number-badge {
  font-family: var(--font-mono);
  font-size: 13px;
  font-weight: 600;
  color: var(--text-secondary);
  background-color: var(--bg-muted);
  border: 1px solid var(--border-subtle);
  padding: 4px 10px;
  border-radius: var(--radius-sm);
  white-space: nowrap;
}

.lab-info-main {
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.lab-title-row {
  display: flex;
  align-items: center;
  gap: 12px;
}

.lab-title-text {
  font-size: 16px;
  font-weight: 600;
  color: var(--text-primary);
}

.lab-app-pill {
  font-size: 12px;
  color: var(--text-muted);
  background-color: var(--bg-muted);
  padding: 2px 8px;
  border-radius: 999px;
  font-weight: 500;
}

.lab-short-desc {
  font-size: 13px;
  color: var(--text-secondary);
  line-height: 1.4;
}

.lab-row-right {
  display: flex;
  align-items: center;
  gap: 16px;
  flex-shrink: 0;
}

/* Difficulty Badges */
.diff-badge {
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  padding: 3px 9px;
  border-radius: 999px;
  white-space: nowrap;
}

.diff-Beginner {
  background-color: var(--badge-beginner-bg);
  color: var(--badge-beginner-text);
  border: 1px solid var(--badge-beginner-border);
}

.diff-Easy {
  background-color: var(--badge-easy-bg);
  color: var(--badge-easy-text);
  border: 1px solid var(--badge-easy-border);
}

.diff-Intermediate {
  background-color: var(--badge-intermediate-bg);
  color: var(--badge-intermediate-text);
  border: 1px solid var(--badge-intermediate-border);
}

.diff-Advanced {
  background-color: var(--badge-advanced-bg);
  color: var(--badge-advanced-text);
  border: 1px solid var(--badge-advanced-border);
}

.diff-Expert {
  background-color: var(--badge-expert-bg);
  color: var(--badge-expert-text);
  border: 1px solid var(--badge-expert-border);
}

.status-badge {
  font-size: 12px;
  font-weight: 500;
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 4px 10px;
  border-radius: var(--radius-sm);
  white-space: nowrap;
}

.status-unsolved {
  color: var(--text-muted);
  background-color: var(--bg-subtle);
  border: 1px solid var(--border-subtle);
}

.status-solved {
  color: #059669;
  background-color: #ecfdf5;
  border: 1px solid #a7f3d0;
  font-weight: 600;
}

/* Methodological Overview Banner (Homepage) */
.methodology-box {
  background-color: var(--bg-subtle);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-xl);
  padding: 36px 32px;
  margin-bottom: 64px;
}

.methodology-title {
  font-size: 18px;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 12px;
}

.methodology-desc {
  font-size: 14px;
  color: var(--text-secondary);
  line-height: 1.6;
  margin-bottom: 24px;
}

.methodology-steps {
  display: flex;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
}

.step-chip {
  background-color: #ffffff;
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: 8px 14px;
  font-size: 13px;
  font-weight: 500;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 8px;
}

.step-chip-num {
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background-color: var(--bg-muted);
  font-size: 11px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-secondary);
}

.step-arrow {
  color: var(--text-light);
  font-size: 14px;
}

/* Global Footer */
.platform-footer {
  margin-top: auto;
  border-top: 1px solid var(--border-subtle);
  background-color: var(--bg-subtle);
  padding: 32px 0;
  color: var(--text-muted);
  font-size: 13px;
}

.footer-content {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.footer-links {
  display: flex;
  gap: 20px;
}

.footer-link {
  color: var(--text-muted);
  text-decoration: none;
}

.footer-link:hover {
  color: var(--text-primary);
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  font-family: inherit;
  font-size: 14px;
  font-weight: 500;
  padding: 8px 16px;
  border-radius: var(--radius-md);
  border: 1px solid transparent;
  cursor: pointer;
  text-decoration: none;
  transition: all 0.15s ease;
}

.btn-primary {
  background-color: var(--text-primary);
  color: #ffffff;
}

.btn-primary:hover {
  background-color: #1f2937;
}

.btn-secondary {
  background-color: #ffffff;
  border-color: var(--border-subtle);
  color: var(--text-primary);
}

.btn-secondary:hover {
  background-color: var(--bg-subtle);
  border-color: var(--border-hover);
}

.btn-sm {
  font-size: 12px;
  padding: 5px 10px;
  border-radius: var(--radius-sm);
}

/* Utilities */
.code-block {
  font-family: var(--font-mono);
  background-color: var(--bg-muted);
  border: 1px solid var(--border-subtle);
  padding: 12px 16px;
  border-radius: var(--radius-md);
  font-size: 13px;
  color: var(--text-primary);
  overflow-x: auto;
  line-height: 1.5;
}

.code-inline {
  font-family: var(--font-mono);
  background-color: var(--bg-muted);
  border: 1px solid var(--border-subtle);
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 12px;
  color: var(--text-primary);
}

/* Responsive */
@media (max-width: 900px) {
  .category-grid {
    grid-template-columns: 1fr;
  }
  .lab-row-card {
    flex-direction: column;
    align-items: flex-start;
  }
  .lab-row-right {
    width: 100%;
    justify-content: space-between;
    border-top: 1px solid var(--border-subtle);
    padding-top: 12px;
  }
}