/* ============================================================
   IDM Official Website Stylesheet (SEO & Performance Optimized)
   ============================================================ */

:root {
  --primary: #2563eb;
  --primary-hover: #1d4ed8;
  --primary-light: #eff6ff;
  --primary-dark: #1e3a8a;
  --accent: #10b981;
  --accent-hover: #059669;
  --accent-light: #ecfdf5;
  --dark-bg: #090d16;
  --dark-card: #111827;
  --dark-card-border: #1f2937;
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #64748b;
  --light-bg: #f8fafc;
  --card-bg: #ffffff;
  --border-color: #e2e8f0;
  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --radius-full: 9999px;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.06), 0 1px 2px rgba(0,0,0,0.04);
  --shadow-md: 0 4px 6px -1px rgba(0,0,0,0.08), 0 2px 4px -2px rgba(0,0,0,0.04);
  --shadow-lg: 0 10px 25px -3px rgba(0,0,0,0.08), 0 4px 6px -4px rgba(0,0,0,0.04);
  --shadow-xl: 0 20px 30px -8px rgba(37,99,235,0.22);
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Courier New", monospace;
  --transition: all 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}

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

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-sans);
  background-color: var(--light-bg);
  color: var(--text-primary);
  line-height: 1.6;
  overflow-x: hidden;
}

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

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

img, svg {
  vertical-align: middle;
  max-width: 100%;
}

/* ============================================================
   Layout & Container
   ============================================================ */
.container {
  width: 100%;
  max-width: 1240px;
  margin-left: auto;
  margin-right: auto;
  padding-left: 24px;
  padding-right: 24px;
}

.section {
  padding: 80px 0;
  position: relative;
}

.section-alt {
  background-color: #ffffff;
  border-top: 1px solid var(--border-color);
  border-bottom: 1px solid var(--border-color);
}

.section-dark {
  background: radial-gradient(circle at 50% 0%, #1e293b 0%, #090d16 100%);
  color: #f8fafc;
  padding: 90px 0;
}

.section-header {
  text-align: center;
  max-width: 760px;
  margin: 0 auto 56px auto;
}

.section-tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 0.85rem;
  font-weight: 700;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  color: var(--primary);
  background-color: var(--primary-light);
  padding: 6px 14px;
  border-radius: var(--radius-full);
  margin-bottom: 16px;
}

.section-dark .section-tag {
  background: rgba(37,99,235,0.25);
  color: #93c5fd;
  border: 1px solid rgba(147,197,253,0.3);
}

.section-title {
  font-size: 2.25rem;
  font-weight: 800;
  line-height: 1.25;
  letter-spacing: -0.02em;
  margin-bottom: 16px;
  color: var(--text-primary);
}

.section-dark .section-title {
  color: #ffffff;
}

.section-desc {
  font-size: 1.125rem;
  color: var(--text-secondary);
  line-height: 1.7;
}

.section-dark .section-desc {
  color: #94a3b8;
}

/* ============================================================
   Navigation Header
   ============================================================ */
.site-header {
  position: sticky;
  top: 0;
  z-index: 1000;
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  border-bottom: 1px solid rgba(226, 232, 240, 0.8);
  transition: var(--transition);
}

.nav-container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 72px;
}

.brand-logo {
  display: flex;
  align-items: center;
  gap: 12px;
  text-decoration: none;
}

.brand-logo svg, .brand-logo img {
  width: 38px;
  height: 38px;
}

.brand-title {
  font-size: 1.25rem;
  font-weight: 800;
  color: #0f172a;
  display: flex;
  flex-direction: column;
  line-height: 1.1;
}

.brand-title span.sub {
  font-size: 0.72rem;
  font-weight: 600;
  color: var(--primary);
  letter-spacing: 0.04em;
}

.nav-menu {
  display: flex;
  align-items: center;
  list-style: none;
  gap: 32px;
}

.nav-link {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-secondary);
  position: relative;
  padding: 6px 0;
}

.nav-link:hover, .nav-link.active {
  color: var(--primary);
}

.nav-link.active::after {
  content: "";
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  height: 2px;
  background-color: var(--primary);
  border-radius: 2px;
}

.nav-actions {
  display: flex;
  align-items: center;
  gap: 16px;
}

.nav-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: 8px;
  color: var(--text-primary);
}

/* ============================================================
   Buttons & CTAs
   ============================================================ */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  font-weight: 700;
  font-size: 1rem;
  padding: 13px 26px;
  border-radius: var(--radius-md);
  cursor: pointer;
  border: none;
  transition: var(--transition);
  text-align: center;
}

.btn-primary {
  background: linear-gradient(135deg, #2563eb 0%, #1d4ed8 100%);
  color: #ffffff;
  box-shadow: 0 4px 14px rgba(37,99,235,0.35);
}

.btn-primary:hover {
  background: linear-gradient(135deg, #1d4ed8 0%, #1e40af 100%);
  color: #ffffff;
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(37,99,235,0.45);
}

.btn-success {
  background: linear-gradient(135deg, #10b981 0%, #059669 100%);
  color: #ffffff;
  box-shadow: 0 4px 14px rgba(16,185,129,0.35);
}

.btn-success:hover {
  background: linear-gradient(135deg, #059669 0%, #047857 100%);
  color: #ffffff;
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(16,185,129,0.45);
}

.btn-outline {
  background-color: transparent;
  color: var(--text-primary);
  border: 1px solid var(--border-color);
}

.btn-outline:hover {
  background-color: #f1f5f9;
  border-color: #cbd5e1;
  color: var(--primary);
}

.btn-lg {
  padding: 16px 34px;
  font-size: 1.125rem;
  border-radius: var(--radius-lg);
}

.btn-sm {
  padding: 8px 16px;
  font-size: 0.875rem;
  border-radius: var(--radius-sm);
}

/* ============================================================
   Hero Section
   ============================================================ */
.hero {
  position: relative;
  padding: 70px 0 90px 0;
  overflow: hidden;
  background: radial-gradient(circle at 80% 20%, rgba(37,99,235,0.08) 0%, transparent 60%),
              radial-gradient(circle at 10% 80%, rgba(16,185,129,0.06) 0%, transparent 60%),
              #ffffff;
  border-bottom: 1px solid var(--border-color);
}

.hero-grid {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 48px;
  align-items: center;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: #eff6ff;
  border: 1px solid #bfdbfe;
  color: #1e40af;
  font-size: 0.875rem;
  font-weight: 600;
  padding: 6px 14px;
  border-radius: var(--radius-full);
  margin-bottom: 24px;
}

.hero-badge .pulse-dot {
  width: 8px;
  height: 8px;
  background-color: #10b981;
  border-radius: 50%;
  animation: pulse 2s infinite;
}

@keyframes pulse {
  0% { transform: scale(0.95); box-shadow: 0 0 0 0 rgba(16,185,129,0.7); }
  70% { transform: scale(1); box-shadow: 0 0 0 6px rgba(16,185,129,0); }
  100% { transform: scale(0.95); box-shadow: 0 0 0 0 rgba(16,185,129,0); }
}

.hero-title {
  font-size: 3.25rem;
  font-weight: 850;
  line-height: 1.15;
  letter-spacing: -0.03em;
  margin-bottom: 20px;
  color: #0f172a;
}

.hero-title .gradient-text {
  background: linear-gradient(135deg, #2563eb 0%, #06b6d4 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.hero-subtitle {
  font-size: 1.25rem;
  color: var(--text-secondary);
  line-height: 1.7;
  margin-bottom: 36px;
  max-width: 600px;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 16px;
  margin-bottom: 28px;
}

.download-meta {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 20px;
  font-size: 0.875rem;
  color: var(--text-muted);
}

.meta-item {
  display: flex;
  align-items: center;
  gap: 6px;
}

.meta-item svg {
  color: var(--accent);
}

/* Hero Right Preview Card */
.hero-card {
  background: linear-gradient(145deg, #1e293b, #0f172a);
  border: 1px solid rgba(255,255,255,0.12);
  border-radius: var(--radius-lg);
  padding: 30px;
  box-shadow: 0 25px 50px -12px rgba(15,23,42,0.35);
  color: #ffffff;
  position: relative;
}

.hero-card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid rgba(255,255,255,0.1);
  padding-bottom: 16px;
  margin-bottom: 20px;
}

.window-controls {
  display: flex;
  gap: 6px;
}

.window-dot {
  width: 12px;
  height: 12px;
  border-radius: 50%;
}
.window-dot.red { background: #ef4444; }
.window-dot.yellow { background: #f59e0b; }
.window-dot.green { background: #10b981; }

.hero-card-title {
  font-size: 0.85rem;
  color: #94a3b8;
  font-weight: 500;
}

.download-status-card {
  background: rgba(255,255,255,0.05);
  border: 1px solid rgba(255,255,255,0.08);
  border-radius: var(--radius-md);
  padding: 20px;
  margin-bottom: 16px;
}

.file-info {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 12px;
}

.file-name {
  font-weight: 700;
  font-size: 1rem;
  color: #f1f5f9;
}

.file-speed {
  font-size: 0.95rem;
  font-weight: 700;
  color: #38bdf8;
  background: rgba(56,189,248,0.15);
  padding: 4px 10px;
  border-radius: var(--radius-full);
}

.progress-container {
  height: 10px;
  background: rgba(255,255,255,0.1);
  border-radius: var(--radius-full);
  overflow: hidden;
  margin-bottom: 12px;
}

.progress-bar {
  height: 100%;
  width: 82%;
  background: linear-gradient(90deg, #10b981, #06b6d4, #3b82f6);
  border-radius: var(--radius-full);
  animation: progressPulse 2s infinite ease-in-out;
}

@keyframes progressPulse {
  0% { opacity: 0.85; }
  50% { opacity: 1; }
  100% { opacity: 0.85; }
}

.progress-meta {
  display: flex;
  justify-content: space-between;
  font-size: 0.8rem;
  color: #94a3b8;
}

.threads-visual {
  display: grid;
  grid-template-columns: repeat(8, 1fr);
  gap: 6px;
  margin-top: 18px;
}

.thread-bar {
  height: 28px;
  background: rgba(59,130,246,0.25);
  border: 1px solid rgba(59,130,246,0.4);
  border-radius: 4px;
  position: relative;
  overflow: hidden;
}

.thread-fill {
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  background: #3b82f6;
  height: 80%;
  animation: threadHeight 3s infinite alternate ease-in-out;
}

@keyframes threadHeight {
  0% { height: 60%; }
  50% { height: 95%; }
  100% { height: 75%; }
}

.card-footer-tip {
  margin-top: 16px;
  font-size: 0.8rem;
  color: #cbd5e1;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

/* ============================================================
   Feature Highlights Grid
   ============================================================ */
.features-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(340px, 1fr));
  gap: 30px;
}

.feature-card {
  background: var(--card-bg);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 36px 30px;
  transition: var(--transition);
  display: flex;
  flex-direction: column;
  box-shadow: var(--shadow-sm);
}

.feature-card:hover {
  transform: translateY(-5px);
  box-shadow: var(--shadow-lg);
  border-color: #cbd5e1;
}

.feature-icon-wrapper {
  width: 58px;
  height: 58px;
  border-radius: var(--radius-md);
  background: var(--primary-light);
  color: var(--primary);
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 22px;
}

.feature-icon-wrapper.green {
  background: var(--accent-light);
  color: var(--accent);
}

.feature-icon-wrapper.purple {
  background: #f5f3ff;
  color: #8b5cf6;
}

.feature-icon-wrapper.orange {
  background: #fff7ed;
  color: #f97316;
}

.feature-icon-wrapper.cyan {
  background: #ecfeff;
  color: #06b6d4;
}

.feature-title {
  font-size: 1.35rem;
  font-weight: 700;
  margin-bottom: 12px;
  color: #0f172a;
}

.feature-desc {
  font-size: 0.95rem;
  color: var(--text-secondary);
  line-height: 1.7;
}

/* ============================================================
   Technical Comparison (IDM vs Traditional)
   ============================================================ */
.comparison-wrapper {
  background: #ffffff;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow-md);
  margin-top: 40px;
}

.comparison-table {
  width: 100%;
  border-collapse: collapse;
  text-align: left;
}

.comparison-table th, .comparison-table td {
  padding: 20px 24px;
  border-bottom: 1px solid var(--border-color);
}

.comparison-table th {
  background-color: #f8fafc;
  font-weight: 700;
  font-size: 1rem;
  color: var(--text-primary);
}

.comparison-table th.highlight, .comparison-table td.highlight {
  background-color: #eff6ff;
  color: #1e3a8a;
  font-weight: 700;
}

.comparison-table tr:last-child td {
  border-bottom: none;
}

.badge-check {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  color: #059669;
  font-weight: 600;
}

.badge-cross {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  color: #dc2626;
  font-weight: 600;
}

/* ============================================================
   Download Section Box
   ============================================================ */
.download-box {
  background: #ffffff;
  border: 2px solid #2563eb;
  border-radius: var(--radius-lg);
  padding: 44px;
  box-shadow: var(--shadow-xl);
  max-width: 980px;
  margin: 0 auto;
}

.download-box-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 20px;
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 28px;
  margin-bottom: 30px;
}

.release-version {
  display: flex;
  align-items: center;
  gap: 16px;
}

.version-badge {
  background: #2563eb;
  color: #ffffff;
  font-weight: 800;
  font-size: 1.25rem;
  padding: 8px 18px;
  border-radius: var(--radius-md);
}

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

.download-grid-actions {
  display: grid;
  grid-template-columns: 1.2fr 0.8fr;
  gap: 30px;
  align-items: center;
}

.download-channel-btn {
  display: flex;
  align-items: center;
  justify-content: space-between;
  background: linear-gradient(135deg, #2563eb 0%, #1d4ed8 100%);
  color: #ffffff;
  padding: 20px 28px;
  border-radius: var(--radius-md);
  font-size: 1.15rem;
  font-weight: 700;
  text-decoration: none;
  box-shadow: 0 8px 20px rgba(37,99,235,0.3);
  transition: var(--transition);
}

.download-channel-btn:hover {
  background: linear-gradient(135deg, #1d4ed8 0%, #1e40af 100%);
  transform: translateY(-2px);
  box-shadow: 0 12px 26px rgba(37,99,235,0.4);
  color: #ffffff;
}

.download-specs-list {
  list-style: none;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
}

.spec-item {
  font-size: 0.9rem;
  color: var(--text-secondary);
}

.spec-item strong {
  color: var(--text-primary);
}

.sha256-box {
  margin-top: 28px;
  padding: 16px 20px;
  background-color: #f8fafc;
  border: 1px dashed #cbd5e1;
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: #334155;
  word-break: break-all;
}

.btn-copy {
  background: #ffffff;
  border: 1px solid var(--border-color);
  padding: 6px 14px;
  border-radius: var(--radius-sm);
  font-family: var(--font-sans);
  font-size: 0.8rem;
  font-weight: 600;
  cursor: pointer;
  white-space: nowrap;
  transition: var(--transition);
}

.btn-copy:hover {
  background: #e2e8f0;
}

/* ============================================================
   Step-by-Step Installation & Tutorial
   ============================================================ */
.steps-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 30px;
}

.step-card {
  background: #ffffff;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 34px 26px;
  position: relative;
  box-shadow: var(--shadow-sm);
  transition: var(--transition);
}

.step-card:hover {
  border-color: #93c5fd;
  box-shadow: var(--shadow-md);
}

.step-number {
  position: absolute;
  top: -16px;
  left: 26px;
  width: 36px;
  height: 36px;
  background: #2563eb;
  color: #ffffff;
  font-weight: 800;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.1rem;
  box-shadow: 0 4px 10px rgba(37,99,235,0.35);
}

.step-card h3 {
  font-size: 1.2rem;
  font-weight: 700;
  margin-top: 10px;
  margin-bottom: 12px;
  color: #0f172a;
}

.step-card p {
  font-size: 0.95rem;
  color: var(--text-secondary);
  line-height: 1.7;
}

/* ============================================================
   Browser Integration Section
   ============================================================ */
.browsers-strip {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 20px;
  margin-top: 36px;
}

.browser-pill {
  display: flex;
  align-items: center;
  gap: 10px;
  background: #ffffff;
  border: 1px solid var(--border-color);
  padding: 12px 22px;
  border-radius: var(--radius-full);
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-primary);
  box-shadow: var(--shadow-sm);
}

.browser-pill svg {
  width: 22px;
  height: 22px;
}

/* ============================================================
   Changelog Section
   ============================================================ */
.changelog-timeline {
  max-width: 860px;
  margin: 0 auto;
  position: relative;
  padding-left: 30px;
}

.changelog-timeline::before {
  content: "";
  position: absolute;
  top: 10px;
  bottom: 10px;
  left: 10px;
  width: 2px;
  background-color: var(--border-color);
}

.changelog-item {
  position: relative;
  margin-bottom: 40px;
}

.changelog-item::before {
  content: "";
  position: absolute;
  left: -26px;
  top: 6px;
  width: 14px;
  height: 14px;
  border-radius: 50%;
  background: var(--primary);
  border: 3px solid #ffffff;
  box-shadow: 0 0 0 2px var(--primary);
}

.changelog-header {
  display: flex;
  align-items: center;
  gap: 14px;
  margin-bottom: 12px;
}

.changelog-version {
  font-size: 1.25rem;
  font-weight: 800;
  color: #0f172a;
}

.changelog-date {
  font-size: 0.85rem;
  color: var(--text-muted);
}

.changelog-content {
  background: #ffffff;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 20px;
  box-shadow: var(--shadow-sm);
}

.changelog-content ul {
  padding-left: 20px;
  color: var(--text-secondary);
  font-size: 0.95rem;
}

.changelog-content li {
  margin-bottom: 6px;
}

/* ============================================================
   Accordion FAQ Section
   ============================================================ */
.faq-list {
  max-width: 860px;
  margin: 0 auto;
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.faq-item {
  background: #ffffff;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  overflow: hidden;
  transition: var(--transition);
}

.faq-item.active {
  border-color: #93c5fd;
  box-shadow: var(--shadow-md);
}

.faq-question {
  width: 100%;
  background: none;
  border: none;
  padding: 22px 26px;
  text-align: left;
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  justify-content: space-between;
  cursor: pointer;
  transition: var(--transition);
}

.faq-question:hover {
  color: var(--primary);
}

.faq-chevron {
  transition: transform 0.3s ease;
  flex-shrink: 0;
  color: var(--text-muted);
}

.faq-item.active .faq-chevron {
  transform: rotate(180deg);
  color: var(--primary);
}

.faq-answer {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.35s ease-out;
  padding: 0 26px;
  color: var(--text-secondary);
  font-size: 0.95rem;
  line-height: 1.7;
}

.faq-answer-inner {
  padding-bottom: 22px;
  border-top: 1px solid #f1f5f9;
  padding-top: 14px;
}

/* ============================================================
   Breadcrumbs & Article Formatting (SEO)
   ============================================================ */
.breadcrumb {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-bottom: 24px;
  list-style: none;
}

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

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

.breadcrumb-separator {
  color: #cbd5e1;
}

/* ============================================================
   Footer
   ============================================================ */
.site-footer {
  background: #090d16;
  color: #94a3b8;
  padding: 64px 0 32px 0;
  border-top: 1px solid #1e293b;
  font-size: 0.9rem;
}

.footer-grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1.5fr;
  gap: 48px;
  margin-bottom: 48px;
}

.footer-brand p {
  margin-top: 14px;
  line-height: 1.7;
  max-width: 320px;
}

.footer-col h4 {
  color: #ffffff;
  font-size: 1rem;
  font-weight: 700;
  margin-bottom: 18px;
}

.footer-links {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.footer-links a {
  color: #94a3b8;
}

.footer-links a:hover {
  color: #ffffff;
}

.footer-bottom {
  border-top: 1px solid #1e293b;
  padding-top: 32px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 16px;
  font-size: 0.85rem;
}

.disclaimer-text {
  font-size: 0.8rem;
  color: #64748b;
  margin-top: 8px;
  line-height: 1.6;
}

/* ============================================================
   Back to top & Toast
   ============================================================ */
.back-to-top {
  position: fixed;
  bottom: 30px;
  right: 30px;
  width: 44px;
  height: 44px;
  background: var(--primary);
  color: #ffffff;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  border: none;
  box-shadow: 0 4px 14px rgba(37,99,235,0.4);
  opacity: 0;
  visibility: hidden;
  transition: var(--transition);
  z-index: 900;
}

.back-to-top.visible {
  opacity: 1;
  visibility: visible;
}

.back-to-top:hover {
  background: var(--primary-hover);
  transform: translateY(-3px);
}

.toast {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%) translateY(100px);
  background: #0f172a;
  color: #ffffff;
  padding: 12px 24px;
  border-radius: var(--radius-md);
  font-size: 0.9rem;
  font-weight: 600;
  box-shadow: var(--shadow-lg);
  opacity: 0;
  transition: transform 0.3s cubic-bezier(0.16, 1, 0.3, 1), opacity 0.3s ease;
  z-index: 2000;
  display: flex;
  align-items: center;
  gap: 8px;
}

.toast.show {
  transform: translateX(-50%) translateY(0);
  opacity: 1;
}

/* ============================================================
   Responsive Breakpoints
   ============================================================ */
@media (max-width: 992px) {
  .hero-grid {
    grid-template-columns: 1fr;
    gap: 40px;
  }
  .hero-title {
    font-size: 2.5rem;
  }
  .steps-grid {
    grid-template-columns: 1fr;
  }
  .download-grid-actions {
    grid-template-columns: 1fr;
  }
  .footer-grid {
    grid-template-columns: 1fr 1fr;
  }
}

@media (max-width: 768px) {
  .section {
    padding: 56px 0;
  }
  .hero {
    padding: 40px 0 60px 0;
  }
  .hero-title {
    font-size: 2.1rem;
  }
  .nav-menu {
    display: none;
    position: absolute;
    top: 72px;
    left: 0;
    right: 0;
    background: #ffffff;
    flex-direction: column;
    padding: 24px;
    border-bottom: 1px solid var(--border-color);
    box-shadow: var(--shadow-lg);
    gap: 16px;
  }
  .nav-menu.open {
    display: flex;
  }
  .nav-toggle {
    display: block;
  }
  .footer-grid {
    grid-template-columns: 1fr;
    gap: 32px;
  }
  .download-box {
    padding: 24px 18px;
  }
  .download-specs-list {
    grid-template-columns: 1fr;
  }
  .sha256-box {
    flex-direction: column;
    align-items: flex-start;
  }
  .btn-copy {
    width: 100%;
  }
}