/* ==========================================================================
   ARTICLE & SEO KNOWLEDGE BASE STYLESHEET — BUYEROS (muanhatayhanoi.vn)
   Typography: Inter · High Readability · Editorial & Data-Driven Layout
   ========================================================================== */

:root {
  --primary: #059669;
  --primary-hover: #047857;
  --primary-dark: #064e3b;
  --primary-light: #ecfdf5;
  --accent: #d97706;
  --accent-light: #fffbeb;
  --danger: #dc2626;
  --danger-light: #fef2f2;
  
  --bg-page: #f8fafc;
  --bg-card: #ffffff;
  --text-main: #0f172a;
  --text-body: #334155;
  --text-muted: #64748b;
  --border: #e2e8f0;

  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  --font-mono: 'JetBrains Mono', Consolas, monospace;
}

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

body {
  font-family: var(--font-sans);
  background-color: var(--bg-page);
  color: var(--text-body);
  line-height: 1.8;
  font-size: 17px;
  -webkit-font-smoothing: antialiased;
}

/* Header */
.header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border);
  padding: 14px 0;
}

.container {
  max-width: 900px;
  margin: 0 auto;
  padding: 0 20px;
}

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

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  color: var(--text-main);
}

.brand-icon {
  width: 32px;
  height: 32px;
  background: linear-gradient(135deg, var(--primary), var(--primary-dark));
  color: #fff;
  border-radius: 6px;
  display: flex;
  align-items: center;
  justify-content: center;
}

.brand-text strong {
  font-size: 16px;
  font-weight: 800;
  display: block;
  line-height: 1.2;
}

.brand-text span {
  font-size: 11px;
  color: var(--text-muted);
}

.btn-header-zalo {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: #f0fdf4;
  color: var(--primary-dark);
  font-weight: 600;
  font-size: 13px;
  padding: 7px 14px;
  border-radius: 999px;
  text-decoration: none;
  border: 1px solid #bbf7d0;
  transition: all 0.2s;
}

/* Article Shell */
.article-shell {
  background: var(--bg-card);
  border-radius: 16px;
  border: 1px solid var(--border);
  box-shadow: 0 4px 20px rgba(0,0,0,0.04);
  padding: 40px 24px;
  margin: 32px auto 60px;
}

@media (min-width: 768px) {
  .article-shell {
    padding: 56px 48px;
  }
}

/* Breadcrumbs */
.breadcrumb {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  font-size: 13px;
  color: var(--text-muted);
  margin-bottom: 24px;
  list-style: none;
}

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

.breadcrumb a:hover {
  text-decoration: underline;
}

.breadcrumb-sep {
  color: #cbd5e1;
}

/* Meta / Author Badge */
.article-meta {
  display: flex;
  align-items: center;
  gap: 14px;
  margin-bottom: 24px;
  padding-bottom: 20px;
  border-bottom: 1px solid var(--border);
}

.author-avatar {
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: var(--primary-light);
  color: var(--primary-dark);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 18px;
}

.author-info strong {
  display: block;
  font-size: 14px;
  color: var(--text-main);
}

.author-info span {
  font-size: 12px;
  color: var(--text-muted);
}

/* Typography */
h1.article-title {
  font-size: 32px;
  font-weight: 800;
  line-height: 1.3;
  color: var(--text-main);
  letter-spacing: -0.02em;
  margin-bottom: 18px;
}

@media (min-width: 768px) {
  h1.article-title {
    font-size: 38px;
  }
}

.article-lead {
  font-size: 19px;
  color: #475569;
  line-height: 1.6;
  font-weight: 500;
  margin-bottom: 32px;
  padding: 16px 20px;
  background: #f8fafc;
  border-left: 4px solid var(--primary);
  border-radius: 4px;
}

h2 {
  font-size: 24px;
  font-weight: 800;
  color: var(--text-main);
  margin: 40px 0 16px;
  letter-spacing: -0.01em;
  padding-bottom: 8px;
  border-bottom: 1px solid #f1f5f9;
}

h3 {
  font-size: 20px;
  font-weight: 700;
  color: var(--text-main);
  margin: 28px 0 12px;
}

p {
  margin-bottom: 20px;
}

ul, ol {
  margin: 0 0 24px 24px;
}

li {
  margin-bottom: 8px;
}

strong {
  color: var(--text-main);
}

/* Data Tables */
.table-wrap {
  overflow-x: auto;
  margin: 28px 0;
  border: 1px solid var(--border);
  border-radius: 8px;
}

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 15px;
}

th, td {
  padding: 12px 16px;
  text-align: left;
}

th {
  background: #f1f5f9;
  font-weight: 700;
  color: var(--text-main);
  border-bottom: 2px solid var(--border);
}

tr:nth-child(even) td {
  background: #f8fafc;
}

tr:not(:last-child) td {
  border-bottom: 1px solid var(--border);
}

/* Callout Box (Warning / Alert / Insight) */
.callout {
  padding: 20px;
  border-radius: 8px;
  margin: 28px 0;
  border-left: 4px solid;
}

.callout-warning {
  background: var(--danger-light);
  border-left-color: var(--danger);
  color: #7f1d1d;
}

.callout-warning strong {
  color: #991b1b;
}

.callout-insight {
  background: var(--accent-light);
  border-left-color: var(--accent);
  color: #78350f;
}

.callout-insight strong {
  color: #92400e;
}

.callout-tool {
  background: var(--primary-light);
  border-left-color: var(--primary);
  color: var(--primary-dark);
}

/* In-Article Tool Banner (High-Converting Bridge) */
.tool-banner {
  background: linear-gradient(135deg, #064e3b 0%, #047857 100%);
  color: #ffffff;
  border-radius: 12px;
  padding: 28px 24px;
  margin: 36px 0;
  text-align: center;
}

.tool-banner h3 {
  color: #ffffff;
  font-size: 22px;
  margin-bottom: 10px;
}

.tool-banner p {
  color: #d1fae5;
  font-size: 15px;
  max-width: 620px;
  margin: 0 auto 20px;
}

.tool-banner a {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: #ffffff;
  color: #065f46;
  font-weight: 700;
  font-size: 15px;
  padding: 12px 24px;
  border-radius: 8px;
  text-decoration: none;
  box-shadow: 0 4px 14px rgba(0,0,0,0.15);
  transition: transform 0.2s;
}

.tool-banner a:hover {
  transform: translateY(-2px);
}

/* FAQ Accordion */
.faq-section {
  margin-top: 48px;
  padding-top: 32px;
  border-top: 2px solid var(--border);
}

.faq-item {
  border: 1px solid var(--border);
  border-radius: 8px;
  margin-bottom: 12px;
  background: #fff;
}

.faq-item summary {
  padding: 16px 20px;
  font-weight: 700;
  font-size: 16px;
  color: var(--text-main);
  cursor: pointer;
  list-style: none;
  position: relative;
}

.faq-item summary::-webkit-details-marker {
  display: none;
}

.faq-item summary::after {
  content: '+';
  position: absolute;
  right: 20px;
  font-size: 20px;
  color: var(--text-muted);
}

.faq-item[open] summary::after {
  content: '−';
}

.faq-answer {
  padding: 0 20px 16px;
  font-size: 15px;
  color: var(--text-body);
}

/* Footer / Author Signoff */
.author-box {
  background: #f8fafc;
  border-radius: 12px;
  padding: 24px;
  margin-top: 40px;
  border: 1px solid var(--border);
  display: flex;
  gap: 16px;
  align-items: center;
}

.author-box img {
  border-radius: 50%;
  width: 64px;
  height: 64px;
}

.author-box h4 {
  font-size: 16px;
  margin-bottom: 4px;
}

.author-box p {
  font-size: 13px;
  color: var(--text-muted);
  margin-bottom: 0;
}