/* ==========================================================================
   FAQHub - Optimized for Google News, Discover & Core Web Vitals
   ========================================================================== */

/* CSS Variables - Modern Color Scheme for News/Content Sites */
:root {
  /* Primary Colors - Professional Blue Theme */
  --color-primary: #1a73e8;
  --color-primary-dark: #0d47a1;
  --color-primary-light: #4285f4;

  /* Accent Colors */
  --color-accent: #ea4335;
  --color-accent-light: #ff6b6b;

  /* Neutral Colors */
  --color-text: #202124;
  --color-text-secondary: #5f6368;
  --color-text-light: #80868b;
  --color-bg: #ffffff;
  --color-bg-secondary: #f8f9fa;
  --color-bg-tertiary: #e8eaed;
  --color-border: #dadce0;

  /* Semantic Colors */
  --color-success: #34a853;
  --color-warning: #fbbc04;
  --color-error: #ea4335;

  /* Typography - Optimized for Vietnamese */
  --font-primary: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-heading: "Inter", "Roboto", -apple-system, BlinkMacSystemFont, sans-serif;

  /* Font Sizes - Scaled for better readability */
  --font-size-xs: 0.75rem;    /* 12px */
  --font-size-sm: 0.875rem;   /* 14px */
  --font-size-base: 0.9375rem; /* 15px - easier to read */
  --font-size-md: 1rem;       /* 16px */
  --font-size-lg: 1.125rem;   /* 18px */
  --font-size-xl: 1.25rem;    /* 20px */
  --font-size-2xl: 1.5rem;    /* 24px */
  --font-size-3xl: 1.875rem;  /* 30px */
  --font-size-4xl: 2.25rem;   /* 36px */

  /* Spacing - More comfortable */
  --spacing-xs: 0.375rem;     /* 6px */
  --spacing-sm: 0.625rem;     /* 10px */
  --spacing-md: 1rem;         /* 16px */
  --spacing-lg: 1.25rem;      /* 20px */
  --spacing-xl: 1.75rem;      /* 28px */
  --spacing-2xl: 2.5rem;      /* 40px */
  --spacing-3xl: 3.5rem;      /* 56px */

  /* Layout */
  --container-max-width: 1140px;
  --container-padding: 1.25rem;
  --border-radius: 8px;
  --border-radius-sm: 4px;
  --border-radius-lg: 12px;

  /* Shadows - Subtle for modern look */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);

  /* Transitions */
  --transition-fast: 150ms ease-in-out;
  --transition-base: 250ms ease-in-out;
  --transition-slow: 350ms ease-in-out;

  /* Z-index scale */
  --z-dropdown: 1000;
  --z-sticky: 1020;
  --z-fixed: 1030;
  --z-modal-backdrop: 1040;
  --z-modal: 1050;
  --z-popover: 1060;
  --z-tooltip: 1070;
}

/* ==========================================================================
   Reset & Base Styles - Optimized for Performance
   ========================================================================== */

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

html {
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-primary);
  font-size: var(--font-size-base);
  line-height: 1.7;
  color: var(--color-text);
  background-color: var(--color-bg-secondary);
  overflow-x: hidden;
  letter-spacing: 0.01em;
}

/* Improve text rendering */
h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-heading);
  font-weight: 700;
  line-height: 1.3;
  color: var(--color-text);
  margin-bottom: var(--spacing-lg);
  letter-spacing: -0.02em;
}

h1 { font-size: var(--font-size-4xl); font-weight: 800; }
h2 { font-size: var(--font-size-3xl); }
h3 { font-size: var(--font-size-2xl); }
h4 { font-size: var(--font-size-xl); font-weight: 600; }
h5 { font-size: var(--font-size-lg); font-weight: 600; }
h6 { font-size: var(--font-size-md); font-weight: 600; }

p {
  margin-bottom: var(--spacing-lg);
  line-height: 1.8;
}

a {
  color: var(--color-primary);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--color-primary-dark);
}

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

/* ==========================================================================
   Layout Components
   ========================================================================== */

.container {
  max-width: var(--container-max-width);
  margin: 0 auto;
  padding: 0 var(--container-padding);
}

.container-fluid {
  width: 100%;
  padding: 0 var(--container-padding);
}

/* ==========================================================================
   Header & Navigation - Sticky for better UX
   ========================================================================== */

.header {
  background-color: var(--color-bg);
  border-bottom: 1px solid var(--color-border);
  position: sticky;
  top: 0;
  z-index: var(--z-sticky);
  box-shadow: var(--shadow-sm);
}

.header__container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--spacing-md) var(--container-padding);
  max-width: var(--container-max-width);
  margin: 0 auto;
}

.header__logo {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--color-primary);
}

.header__logo-icon {
  width: 32px;
  height: 32px;
  background: linear-gradient(135deg, var(--color-primary), var(--color-primary-light));
  border-radius: var(--border-radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  font-weight: bold;
}

.nav {
  display: flex;
  gap: var(--spacing-lg);
  align-items: center;
}

.nav__list {
  display: flex;
  list-style: none;
  gap: var(--spacing-lg);
  margin: 0;
}

.nav__link {
  color: var(--color-text);
  font-weight: 500;
  padding: var(--spacing-sm) var(--spacing-md);
  border-radius: var(--border-radius-sm);
  transition: all var(--transition-fast);
}

.nav__link:hover,
.nav__link--active {
  color: var(--color-primary);
  background-color: var(--color-bg-secondary);
}

.nav__toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: var(--spacing-sm);
}

.nav__toggle-icon {
  width: 24px;
  height: 2px;
  background-color: var(--color-text);
  display: block;
  position: relative;
  transition: background-color var(--transition-fast);
}

.nav__toggle-icon::before,
.nav__toggle-icon::after {
  content: '';
  position: absolute;
  width: 24px;
  height: 2px;
  background-color: var(--color-text);
  transition: all var(--transition-fast);
}

.nav__toggle-icon::before {
  top: -8px;
}

.nav__toggle-icon::after {
  bottom: -8px;
}

/* Search Bar */
.search {
  display: flex;
  align-items: center;
  background-color: var(--color-bg-secondary);
  border-radius: var(--border-radius-lg);
  padding: var(--spacing-sm) var(--spacing-md);
  min-width: 300px;
}

.search__input {
  border: none;
  background: transparent;
  outline: none;
  flex: 1;
  font-size: 0.9rem;
  color: var(--color-text);
}

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

/* ==========================================================================
   Hero Section
   ========================================================================== */

.hero {
  background: linear-gradient(135deg, var(--color-primary-dark) 0%, var(--color-primary) 100%);
  color: white;
  padding: var(--spacing-3xl) 0;
  text-align: center;
}

.hero__title {
  color: white;
  font-size: 3rem;
  margin-bottom: var(--spacing-lg);
  font-weight: 700;
}

.hero__subtitle {
  font-size: 1.25rem;
  opacity: 0.9;
  max-width: 600px;
  margin: 0 auto var(--spacing-xl);
}

.hero__search {
  max-width: 600px;
  margin: 0 auto;
  background-color: white;
  border-radius: var(--border-radius-lg);
  padding: var(--spacing-sm);
  display: flex;
  box-shadow: var(--shadow-xl);
}

.hero__search-input {
  flex: 1;
  border: none;
  outline: none;
  padding: var(--spacing-md);
  font-size: 1rem;
}

.hero__search-button {
  background-color: var(--color-primary);
  color: white;
  border: none;
  padding: var(--spacing-md) var(--spacing-xl);
  border-radius: var(--border-radius);
  font-weight: 600;
  cursor: pointer;
  transition: background-color var(--transition-fast);
}

.hero__search-button:hover {
  background-color: var(--color-primary-dark);
}

/* ==========================================================================
   Category Tabs/Pills
   ========================================================================== */

.categories {
  background-color: var(--color-bg);
  padding: var(--spacing-lg) 0;
  border-bottom: 1px solid var(--color-border);
  position: sticky;
  top: 73px;
  z-index: var(--z-sticky);
}

.categories__list {
  display: flex;
  gap: var(--spacing-md);
  list-style: none;
  overflow-x: auto;
  padding-bottom: var(--spacing-sm);
  scrollbar-width: thin;
}

.categories__list::-webkit-scrollbar {
  height: 4px;
}

.categories__list::-webkit-scrollbar-thumb {
  background-color: var(--color-border);
  border-radius: 2px;
}

.category-pill {
  padding: var(--spacing-sm) var(--spacing-lg);
  border-radius: var(--border-radius-lg);
  background-color: var(--color-bg-secondary);
  color: var(--color-text);
  font-weight: 500;
  white-space: nowrap;
  cursor: pointer;
  transition: all var(--transition-fast);
  border: 1px solid transparent;
}

.category-pill:hover {
  background-color: var(--color-primary-light);
  color: white;
}

.category-pill--active {
  background-color: var(--color-primary);
  color: white;
}

/* ==========================================================================
   Main Content Area
   ========================================================================== */

.main {
  padding: var(--spacing-2xl) 0;
}

.section {
  margin-bottom: var(--spacing-3xl);
}

.section__header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: var(--spacing-xl);
}

.section__title {
  font-size: 1.75rem;
  font-weight: 700;
  color: var(--color-text);
  position: relative;
  padding-bottom: var(--spacing-sm);
}

.section__title::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 60px;
  height: 3px;
  background-color: var(--color-primary);
  border-radius: 2px;
}

.section__link {
  color: var(--color-primary);
  font-weight: 600;
  display: flex;
  align-items: center;
  gap: var(--spacing-xs);
}

/* ==========================================================================
   Card Grid - News Style Layout
   ========================================================================== */

.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: var(--spacing-xl);
}

.card-grid--featured {
  grid-template-columns: repeat(12, 1fr);
}

.card {
  background-color: var(--color-bg);
  border-radius: var(--border-radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow-md);
  transition: all var(--transition-base);
  display: flex;
  flex-direction: column;
  height: 100%;
}

.card:hover {
  box-shadow: var(--shadow-xl);
  transform: translateY(-4px);
}

.card--featured {
  grid-column: span 8;
}

.card--featured .card__image {
  height: 400px;
}

.card--sidebar {
  grid-column: span 4;
}

.card__image-container {
  position: relative;
  overflow: hidden;
  background-color: var(--color-bg-tertiary);
}

.card__image {
  width: 100%;
  height: 220px;
  object-fit: cover;
  transition: transform var(--transition-slow);
}

.card:hover .card__image {
  transform: scale(1.05);
}

.card__badge {
  position: absolute;
  top: var(--spacing-md);
  left: var(--spacing-md);
  background-color: var(--color-primary);
  color: white;
  padding: var(--spacing-xs) var(--spacing-md);
  border-radius: var(--border-radius-sm);
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.card__content {
  padding: var(--spacing-lg);
  flex: 1;
  display: flex;
  flex-direction: column;
}

.card__meta {
  display: flex;
  align-items: center;
  gap: var(--spacing-md);
  margin-bottom: var(--spacing-md);
  font-size: 0.875rem;
  color: var(--color-text-secondary);
}

.card__category {
  color: var(--color-primary);
  font-weight: 600;
}

.card__date {
  display: flex;
  align-items: center;
  gap: var(--spacing-xs);
}

.card__title {
  font-size: 1.25rem;
  font-weight: 600;
  margin-bottom: var(--spacing-md);
  color: var(--color-text);
  line-height: 1.4;
}

.card--featured .card__title {
  font-size: 2rem;
}

.card__excerpt {
  color: var(--color-text-secondary);
  line-height: 1.6;
  margin-bottom: var(--spacing-lg);
  flex: 1;
}

.card__footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-top: var(--spacing-md);
  border-top: 1px solid var(--color-border);
}

.card__author {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
}

.card__author-avatar {
  width: 32px;
  height: 32px;
  border-radius: 50%;
  background-color: var(--color-bg-tertiary);
}

.card__author-name {
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--color-text);
}

.card__stats {
  display: flex;
  gap: var(--spacing-md);
  font-size: 0.875rem;
  color: var(--color-text-secondary);
}

.card__stat {
  display: flex;
  align-items: center;
  gap: var(--spacing-xs);
}

/* ==========================================================================
   Sidebar Cards (Compact Style)
   ========================================================================== */

.sidebar-cards {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-lg);
}

.sidebar-card {
  background-color: var(--color-bg);
  border-radius: var(--border-radius);
  padding: var(--spacing-lg);
  box-shadow: var(--shadow-sm);
}

.sidebar-card__title {
  font-size: 1.125rem;
  font-weight: 600;
  margin-bottom: var(--spacing-md);
}

.sidebar-list {
  list-style: none;
}

.sidebar-list__item {
  padding: var(--spacing-md) 0;
  border-bottom: 1px solid var(--color-border);
}

.sidebar-list__item:last-child {
  border-bottom: none;
}

.sidebar-list__link {
  display: flex;
  gap: var(--spacing-md);
  color: var(--color-text);
  transition: color var(--transition-fast);
}

.sidebar-list__link:hover {
  color: var(--color-primary);
}

.sidebar-list__number {
  font-weight: 700;
  color: var(--color-primary);
  min-width: 24px;
}

.sidebar-list__text {
  flex: 1;
  font-size: 0.9rem;
  line-height: 1.4;
}

/* ==========================================================================
   FAQ Detail Page
   ========================================================================== */

.article {
  background-color: var(--color-bg);
  border-radius: var(--border-radius-lg);
  padding: var(--spacing-2xl);
  margin-bottom: var(--spacing-xl);
  box-shadow: var(--shadow-md);
}

.article__header {
  margin-bottom: var(--spacing-xl);
  padding-bottom: var(--spacing-xl);
  border-bottom: 2px solid var(--color-border);
}

.article__breadcrumb {
  display: flex;
  gap: var(--spacing-sm);
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  margin-bottom: var(--spacing-lg);
  flex-wrap: wrap;
}

.article__breadcrumb-link {
  color: var(--color-primary);
}

.article__title {
  font-size: 2.5rem;
  line-height: 1.2;
  margin-bottom: var(--spacing-lg);
}

.article__meta {
  display: flex;
  align-items: center;
  gap: var(--spacing-lg);
  flex-wrap: wrap;
}

.article__author {
  display: flex;
  align-items: center;
  gap: var(--spacing-md);
}

.article__author-avatar {
  width: 48px;
  height: 48px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--color-primary), var(--color-primary-light));
}

.article__author-info {
  display: flex;
  flex-direction: column;
}

.article__author-name {
  font-weight: 600;
  color: var(--color-text);
}

.article__author-role {
  font-size: 0.875rem;
  color: var(--color-text-secondary);
}

.article__date {
  font-size: 0.875rem;
  color: var(--color-text-secondary);
}

.article__featured-image {
  width: 100%;
  height: auto;
  max-height: 500px;
  object-fit: cover;
  border-radius: var(--border-radius-lg);
  margin-bottom: var(--spacing-xl);
}

.article__content {
  font-size: 1.125rem;
  line-height: 1.8;
  color: var(--color-text);
}

.article__content h2 {
  margin-top: var(--spacing-2xl);
  margin-bottom: var(--spacing-lg);
  padding-top: var(--spacing-lg);
  border-top: 1px solid var(--color-border);
}

.article__content h3 {
  margin-top: var(--spacing-xl);
  margin-bottom: var(--spacing-md);
}

.article__content p {
  margin-bottom: var(--spacing-lg);
}

.article__content ul,
.article__content ol {
  margin-bottom: var(--spacing-lg);
  padding-left: var(--spacing-xl);
}

.article__content li {
  margin-bottom: var(--spacing-sm);
}

.article__content code {
  background-color: var(--color-bg-secondary);
  padding: 2px 6px;
  border-radius: var(--border-radius-sm);
  font-size: 0.9em;
  font-family: 'Courier New', monospace;
}

.article__content pre {
  background-color: var(--color-text);
  color: var(--color-bg);
  padding: var(--spacing-lg);
  border-radius: var(--border-radius);
  overflow-x: auto;
  margin-bottom: var(--spacing-lg);
}

.article__content blockquote {
  border-left: 4px solid var(--color-primary);
  padding-left: var(--spacing-lg);
  margin: var(--spacing-xl) 0;
  font-style: italic;
  color: var(--color-text-secondary);
}

/* Table of Contents */
.toc {
  background-color: var(--color-bg-secondary);
  border-radius: var(--border-radius-lg);
  padding: var(--spacing-xl);
  margin-bottom: var(--spacing-xl);
}

.toc__title {
  font-size: 1.25rem;
  font-weight: 600;
  margin-bottom: var(--spacing-md);
}

.toc__list {
  list-style: none;
}

.toc__item {
  margin-bottom: var(--spacing-sm);
}

.toc__link {
  color: var(--color-text);
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  padding: var(--spacing-sm);
  border-radius: var(--border-radius-sm);
  transition: all var(--transition-fast);
}

.toc__link:hover {
  background-color: var(--color-bg);
  color: var(--color-primary);
}

/* Related Articles */
.related {
  margin-top: var(--spacing-3xl);
}

.related__title {
  font-size: 1.75rem;
  margin-bottom: var(--spacing-xl);
}

/* ==========================================================================
   Footer
   ========================================================================== */

.footer {
  background-color: var(--color-text);
  color: white;
  padding: var(--spacing-3xl) 0 var(--spacing-xl);
  margin-top: var(--spacing-3xl);
}

.footer__container {
  max-width: var(--container-max-width);
  margin: 0 auto;
  padding: 0 var(--container-padding);
}

.footer__grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: var(--spacing-2xl);
  margin-bottom: var(--spacing-2xl);
}

.footer__section-title {
  color: white;
  font-size: 1.125rem;
  margin-bottom: var(--spacing-lg);
}

.footer__list {
  list-style: none;
}

.footer__list-item {
  margin-bottom: var(--spacing-sm);
}

.footer__link {
  color: rgba(255, 255, 255, 0.8);
  transition: color var(--transition-fast);
}

.footer__link:hover {
  color: white;
}

.footer__bottom {
  border-top: 1px solid rgba(255, 255, 255, 0.1);
  padding-top: var(--spacing-xl);
  text-align: center;
  color: rgba(255, 255, 255, 0.6);
}

/* ==========================================================================
   Utility Classes
   ========================================================================== */

.text-center { text-align: center; }
.text-right { text-align: right; }
.text-left { text-align: left; }

.mt-0 { margin-top: 0; }
.mt-1 { margin-top: var(--spacing-sm); }
.mt-2 { margin-top: var(--spacing-md); }
.mt-3 { margin-top: var(--spacing-lg); }
.mt-4 { margin-top: var(--spacing-xl); }

.mb-0 { margin-bottom: 0; }
.mb-1 { margin-bottom: var(--spacing-sm); }
.mb-2 { margin-bottom: var(--spacing-md); }
.mb-3 { margin-bottom: var(--spacing-lg); }
.mb-4 { margin-bottom: var(--spacing-xl); }

/* ==========================================================================
   Responsive Design - Mobile First
   ========================================================================== */

@media (max-width: 768px) {
  :root {
    --container-padding: 1rem;
  }

  h1 { font-size: 2rem; }
  h2 { font-size: 1.75rem; }
  h3 { font-size: 1.5rem; }

  .hero__title {
    font-size: 2rem;
  }

  .hero__subtitle {
    font-size: 1rem;
  }

  .search {
    display: none;
  }

  .nav__list {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background-color: var(--color-bg);
    flex-direction: column;
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-lg);
    gap: var(--spacing-sm);
  }

  .nav__list--active {
    display: flex;
  }

  .nav__toggle {
    display: block;
  }

  .categories {
    top: 65px;
  }

  .card-grid {
    grid-template-columns: 1fr;
    gap: var(--spacing-lg);
  }

  .card-grid--featured {
    grid-template-columns: 1fr;
  }

  .card--featured,
  .card--sidebar {
    grid-column: span 1;
  }

  .card--featured .card__image {
    height: 250px;
  }

  .article {
    padding: var(--spacing-lg);
  }

  .article__title {
    font-size: 1.75rem;
  }

  .article__content {
    font-size: 1rem;
  }

  .footer__grid {
    grid-template-columns: 1fr;
    gap: var(--spacing-xl);
  }
}

@media (max-width: 480px) {
  .hero {
    padding: var(--spacing-2xl) 0;
  }

  .hero__title {
    font-size: 1.75rem;
  }

  .category-pill {
    font-size: 0.875rem;
    padding: var(--spacing-xs) var(--spacing-md);
  }

  .card__title {
    font-size: 1.125rem;
  }

  .article__title {
    font-size: 1.5rem;
  }
}

/* ==========================================================================
   Performance Optimizations
   ========================================================================== */

/* Reduce motion for users who prefer it */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}

/* Loading skeleton for images */
.skeleton {
  background: linear-gradient(
    90deg,
    var(--color-bg-tertiary) 25%,
    var(--color-bg-secondary) 50%,
    var(--color-bg-tertiary) 75%
  );
  background-size: 200% 100%;
  animation: loading 1.5s ease-in-out infinite;
}

@keyframes loading {
  0% {
    background-position: 200% 0;
  }
  100% {
    background-position: -200% 0;
  }
}

/* Lazy loading images */
img[loading="lazy"] {
  opacity: 0;
  transition: opacity var(--transition-base);
}

img[loading="lazy"].loaded {
  opacity: 1;
}