/* ══ RESET & MODERN DESIGN TOKENS (SLEEK MINIMAL WHITE) ══ */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --bg-main: #ffffff;
  --bg-subtle: #fafafa;
  --bg-card: #ffffff;
  --bg-elevated: #ffffff;
  --bg-input: #ffffff;
  --bg-hover: #f4f4f5;
  --border-light: #e4e4e7;
  --border-focus: #18181b;
  --border-subtle: #f1f1f4;
  --text-primary: #09090b;
  --text-secondary: #52525b;
  --text-tertiary: #a1a1aa;
  --accent: #2563eb;
  --accent-soft: #eff6ff;
  --accent-border: #bfdbfe;
  --success: #16a34a;
  --success-soft: #f0fdf4;
  --warning: #ea580c;
  --warning-soft: #fff7ed;
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;
  --radius-full: 9999px;
  --shadow-subtle: 0 1px 3px rgba(0,0,0,0.03), 0 4px 12px rgba(0,0,0,0.02);
  --shadow-card: 0 4px 20px -2px rgba(0,0,0,0.04), 0 2px 6px -1px rgba(0,0,0,0.02);
  --font-sans: 'Plus Jakarta Sans', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'JetBrains Mono', monospace;
}

body {
  background-color: var(--bg-main);
  color: var(--text-primary);
  font-family: var(--font-sans);
  font-size: 14px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  min-height: 100vh;
}

/* ══ HEADER / NAV (RESPONSIVE) ══ */
.st-header {
  border-bottom: 1px solid var(--border-light);
  background: rgba(255, 255, 255, 0.96);
  backdrop-filter: blur(12px);
  position: sticky;
  top: 0;
  z-index: 50;
}
.st-header-container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 20px;
  height: 60px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.st-brand {
  display: flex;
  align-items: center;
  gap: 8px;
  text-decoration: none;
  color: var(--text-primary);
  font-weight: 700;
  font-size: 15px;
  letter-spacing: -0.3px;
}
.st-brand-badge {
  background: var(--bg-hover);
  border: 1px solid var(--border-light);
  color: var(--text-secondary);
  font-size: 11px;
  font-weight: 600;
  padding: 2px 7px;
  border-radius: var(--radius-full);
}
.st-nav-links {
  display: flex;
  align-items: center;
  gap: 16px;
}
.st-nav-link {
  color: var(--text-secondary);
  text-decoration: none;
  font-size: 13px;
  font-weight: 600;
  transition: color 0.15s ease;
}
.st-nav-link:hover {
  color: var(--text-primary);
}
.st-back-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: #f4f4f5;
  border: 1px solid var(--border-light);
  padding: 6px 12px;
  border-radius: 8px;
  font-size: 12px;
  font-weight: 700;
  color: var(--text-primary);
  text-decoration: none;
  transition: all 0.15s ease;
}
.st-back-btn:hover {
  background: #e4e4e7;
}

/* ══ MAIN LAYOUT (RESPONSIVE) ══ */
.st-main {
  max-width: 1200px;
  margin: 0 auto;
  padding: 32px 20px 80px;
}
@media (max-width: 640px) {
  .st-main {
    padding: 20px 14px 60px;
  }
}

.st-hero {
  text-align: center;
  max-width: 820px;
  margin: 0 auto 36px;
}
.st-hero-tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: #f4f4f5;
  border: 1px solid var(--border-light);
  padding: 4px 12px;
  border-radius: var(--radius-full);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.2px;
  color: var(--text-secondary);
  margin-bottom: 14px;
}
.st-hero-tag svg {
  color: var(--accent);
}
.st-hero-title {
  font-size: clamp(24px, 5.5vw, 36px);
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.2;
  margin-bottom: 12px;
  color: var(--text-primary);
}
.st-hero-subtitle {
  font-size: clamp(14px, 2.5vw, 15px);
  color: var(--text-secondary);
  line-height: 1.6;
}

/* ══ TWO COLUMN APP GRID (STACKS ON TABLETS / PHONES) ══ */
.st-calc-grid {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 24px;
  align-items: start;
}
@media (max-width: 960px) {
  .st-calc-grid {
    grid-template-columns: 1fr;
    gap: 20px;
  }
}

/* ══ WHITE CARD DESIGN ══ */
.st-card {
  background: var(--bg-card);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-card);
  overflow: hidden;
}
.st-card-header {
  padding: 18px 20px;
  border-bottom: 1px solid var(--border-light);
  display: flex;
  align-items: center;
  justify-content: space-between;
  background: #ffffff;
  flex-wrap: wrap;
  gap: 8px;
}
.st-card-title {
  font-size: 15px;
  font-weight: 700;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 8px;
  letter-spacing: -0.2px;
}
.st-card-body {
  padding: 20px;
}
@media (max-width: 640px) {
  .st-card-body {
    padding: 16px;
  }
  .st-card-header {
    padding: 16px;
  }
}

/* ══ TABS / SEGMENTED CONTROLS ══ */
.st-tabs {
  display: flex;
  background: #f4f4f5;
  padding: 4px;
  border-radius: var(--radius-md);
  margin-bottom: 20px;
  gap: 4px;
}
.st-tab-btn {
  flex: 1;
  border: none;
  background: transparent;
  padding: 9px 12px;
  border-radius: 10px;
  font-size: 13px;
  font-weight: 700;
  font-family: var(--font-sans);
  color: var(--text-secondary);
  cursor: pointer;
  transition: all 0.2s ease;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  white-space: nowrap;
}
.st-tab-btn.active {
  background: #ffffff;
  color: var(--text-primary);
  box-shadow: 0 1px 3px rgba(0,0,0,0.06);
}
@media (max-width: 480px) {
  .st-tab-btn {
    font-size: 12px;
    padding: 8px 6px;
  }
}

/* ══ PRESETS PILL ROW (TOUCH RESPONSIVE) ══ */
.st-presets-label {
  font-size: 11px;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.6px;
  color: var(--text-tertiary);
  margin-bottom: 10px;
}
.st-presets-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(130px, 1fr));
  gap: 8px;
  margin-bottom: 22px;
}
@media (max-width: 520px) {
  .st-presets-grid {
    grid-template-columns: 1fr 1fr;
  }
}
.st-preset-btn {
  border: 1px solid var(--border-light);
  background: #ffffff;
  padding: 10px 12px;
  border-radius: var(--radius-sm);
  text-align: left;
  cursor: pointer;
  transition: all 0.15s ease;
  font-family: var(--font-sans);
  min-height: 48px;
}
.st-preset-btn:hover {
  border-color: var(--text-tertiary);
  background: var(--bg-subtle);
}
.st-preset-btn.active {
  border-color: var(--accent);
  background: #eff6ff;
  box-shadow: 0 0 0 1px var(--accent);
}
.st-preset-name {
  font-size: 12px;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 2px;
}
.st-preset-desc {
  font-size: 11px;
  color: var(--text-secondary);
  font-weight: 500;
}

/* ══ FORM CONTROLS & INPUTS ══ */
.st-form-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
  margin-bottom: 18px;
}
@media (max-width: 600px) {
  .st-form-row {
    grid-template-columns: 1fr;
    margin-bottom: 14px;
  }
}
.st-form-group {
  margin-bottom: 18px;
}
.st-form-group:last-child {
  margin-bottom: 0;
}
.st-label {
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: 13px;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 8px;
  flex-wrap: wrap;
  gap: 4px;
}
.st-label-hint {
  font-size: 11px;
  font-weight: 500;
  color: var(--text-secondary);
}
.st-input-wrapper {
  position: relative;
  display: flex;
  align-items: center;
}
.st-input {
  width: 100%;
  padding: 12px 14px;
  padding-right: 68px;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  background: var(--bg-input);
  color: var(--text-primary);
  font-size: 16px;
  font-family: var(--font-sans);
  font-weight: 700;
  letter-spacing: -0.2px;
  outline: none;
  transition: border-color 0.15s ease, box-shadow 0.15s ease;
  min-height: 48px;
}
.st-input:focus {
  border-color: var(--border-focus);
  box-shadow: 0 0 0 3px rgba(0, 0, 0, 0.05);
}
.st-unit-tag {
  position: absolute;
  right: 12px;
  padding: 4px 8px;
  background: #f4f4f5;
  border-radius: var(--radius-sm);
  font-size: 11px;
  font-weight: 800;
  color: var(--text-secondary);
  font-family: var(--font-sans);
}

.st-select {
  width: 100%;
  padding: 12px 14px;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  background: var(--bg-input);
  color: var(--text-primary);
  font-size: 14px;
  font-family: var(--font-sans);
  font-weight: 600;
  outline: none;
  cursor: pointer;
  appearance: none;
  min-height: 48px;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 24 24' fill='none' stroke='%2371717a' stroke-width='2'%3E%3Cpath d='m6 9 6 6 6-6'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 14px center;
  transition: border-color 0.15s ease;
}
.st-select:focus {
  border-color: var(--border-focus);
}

/* ══ RANGE SLIDER ══ */
.st-range-wrap {
  margin-top: 8px;
}
.st-range {
  width: 100%;
  height: 6px;
  background: #e4e4e7;
  border-radius: var(--radius-full);
  outline: none;
  appearance: none;
  cursor: pointer;
}
.st-range::-webkit-slider-thumb {
  appearance: none;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: #09090b;
  border: 2px solid #ffffff;
  box-shadow: 0 1px 4px rgba(0,0,0,0.3);
  cursor: pointer;
  transition: transform 0.1s ease;
}
.st-range::-webkit-slider-thumb:hover {
  transform: scale(1.15);
}

/* ══ LIVE RESULTS SUMMARY CARD ══ */
.st-results-panel {
  background: #fafafa;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  padding: 20px;
  margin-bottom: 18px;
}
.st-results-hero {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  margin-bottom: 16px;
  flex-wrap: wrap;
  gap: 10px;
}
.st-results-title {
  font-size: 11px;
  font-weight: 800;
  color: var(--text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.6px;
}
.st-if-display {
  font-family: var(--font-sans);
  font-size: clamp(30px, 6vw, 42px);
  font-weight: 800;
  color: var(--text-primary);
  letter-spacing: -0.03em;
  line-height: 1.1;
  margin-top: 4px;
}
.st-if-unit {
  font-size: clamp(16px, 3.5vw, 20px);
  font-weight: 700;
  color: var(--text-secondary);
  margin-left: 4px;
}

.st-status-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 6px 12px;
  border-radius: var(--radius-full);
  font-size: 12px;
  font-weight: 700;
  font-family: var(--font-sans);
}
.st-status-badge.valid {
  background: var(--success-soft);
  color: var(--success);
  border: 1px solid #bbf7d0;
}
.st-status-badge.invalid {
  background: var(--warning-soft);
  color: var(--warning);
  border: 1px solid #fed7aa;
}

/* ══ METRICS GRID (RESPONSIVE) ══ */
.st-metrics-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 10px;
  margin-top: 16px;
  padding-top: 16px;
  border-top: 1px solid var(--border-light);
}
@media (max-width: 480px) {
  .st-metrics-grid {
    grid-template-columns: 1fr 1fr;
    gap: 8px;
  }
}
.st-metric-box {
  background: #ffffff;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-sm);
  padding: 10px 12px;
}
.st-metric-lbl {
  font-size: 11px;
  color: var(--text-secondary);
  font-weight: 700;
  margin-bottom: 4px;
}
.st-metric-val {
  font-family: var(--font-sans);
  font-size: 13px;
  font-weight: 700;
  color: var(--text-primary);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

/* ══ SPECTRUM VISUALIZER ══ */
.st-spectrum-box {
  background: #ffffff;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  padding: 18px;
  margin-top: 18px;
}
.st-spectrum-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 12px;
}
.st-spectrum-title {
  font-size: 13px;
  font-weight: 700;
  color: var(--text-primary);
}
.st-spectrum-bar-wrap {
  position: relative;
  height: 44px;
  background: #f4f4f5;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-light);
  overflow: hidden;
  margin-bottom: 8px;
}
.st-spectrum-band-tuner {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0%;
  width: 100%;
  background: rgba(37, 99, 235, 0.08);
  border-left: 2px solid var(--accent);
  border-right: 2px solid var(--accent);
}
.st-spectrum-needle {
  position: absolute;
  top: 0;
  bottom: 0;
  width: 3px;
  background: #09090b;
  transform: translateX(-50%);
  transition: left 0.2s cubic-bezier(0.16, 1, 0.3, 1);
  z-index: 10;
}
.st-spectrum-needle::after {
  content: '';
  position: absolute;
  top: 0;
  left: 50%;
  transform: translateX(-50%);
  width: 9px;
  height: 9px;
  background: #09090b;
  border-radius: 50%;
}
.st-spectrum-labels {
  display: flex;
  justify-content: space-between;
  font-family: var(--font-sans);
  font-size: 11px;
  color: var(--text-tertiary);
  font-weight: 600;
}

/* ══ CHANNEL TABLE (TOUCH SCROLLABLE) ══ */
.st-table-wrap {
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
  margin-top: 14px;
}
.st-table {
  width: 100%;
  min-width: 640px;
  border-collapse: collapse;
  font-size: 13px;
  text-align: left;
}
.st-table th {
  background: #fafafa;
  padding: 11px 14px;
  font-size: 11px;
  font-weight: 800;
  color: var(--text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.6px;
  border-bottom: 1px solid var(--border-light);
}
.st-table td {
  padding: 12px 14px;
  border-bottom: 1px solid var(--border-subtle);
  color: var(--text-primary);
  font-family: var(--font-sans);
  font-weight: 500;
}
.st-table tr:hover td {
  background: #fafafa;
}

/* ══ ACTION BUTTONS ══ */
.st-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 10px 18px;
  border-radius: var(--radius-md);
  font-size: 13px;
  font-weight: 700;
  font-family: var(--font-sans);
  border: 1px solid transparent;
  cursor: pointer;
  transition: all 0.15s ease;
  text-decoration: none;
}
.st-btn-primary {
  background: #09090b;
  color: #ffffff;
}
.st-btn-primary:hover {
  background: #27272a;
}
.st-btn-secondary {
  background: #ffffff;
  color: var(--text-primary);
  border-color: var(--border-light);
}
.st-btn-secondary:hover {
  background: var(--bg-hover);
}

/* ══ FORMULA EXPLANATION CARD ══ */
.st-formula-box {
  background: #fcfcfd;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  padding: 18px;
  margin-top: 20px;
}
.st-formula-box code {
  font-family: var(--font-mono);
  background: #f4f4f5;
  padding: 3px 8px;
  border-radius: 6px;
  font-size: 13px;
  font-weight: 600;
  color: #09090b;
}

/* ══ EXTENDED SEO CONTENT & ENGINEERING REFERENCE GUIDE ══ */
.st-guide-section {
  max-width: 960px;
  margin: 56px auto 0;
  padding-top: 40px;
  border-top: 1px solid var(--border-light);
}
.st-guide-header {
  text-align: center;
  max-width: 720px;
  margin: 0 auto 36px;
}
.st-guide-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: #f4f4f5;
  border: 1px solid var(--border-light);
  padding: 4px 12px;
  border-radius: var(--radius-full);
  font-size: 11px;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.6px;
  color: var(--text-secondary);
  margin-bottom: 12px;
}
.st-guide-title {
  font-size: clamp(22px, 4vw, 28px);
  font-weight: 800;
  letter-spacing: -0.02em;
  margin-bottom: 12px;
  color: var(--text-primary);
}
.st-guide-subtitle {
  font-size: 15px;
  color: var(--text-secondary);
  line-height: 1.6;
}

.st-article-card {
  background: #ffffff;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-lg);
  padding: 26px;
  margin-bottom: 24px;
  box-shadow: var(--shadow-subtle);
}
@media (max-width: 640px) {
  .st-article-card {
    padding: 20px 16px;
  }
}
.st-article-h3 {
  font-size: 18px;
  font-weight: 800;
  letter-spacing: -0.2px;
  color: var(--text-primary);
  margin-bottom: 12px;
  display: flex;
  align-items: center;
  gap: 8px;
}
.st-article-h3 svg {
  color: var(--accent);
  flex-shrink: 0;
}
.st-article-p {
  font-size: 14.5px;
  line-height: 1.75;
  color: var(--text-secondary);
  margin-bottom: 14px;
}
.st-article-p:last-child {
  margin-bottom: 0;
}

/* ══ SPECTRUM ALLOCATION TABLE (RESPONSIVE) ══ */
.st-spec-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 12px;
  margin: 18px 0;
}
.st-spec-item {
  background: #fafafa;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  padding: 14px;
}
.st-spec-item-title {
  font-size: 13.5px;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 6px;
  display: flex;
  justify-content: space-between;
}
.st-spec-item-badge {
  font-size: 11.5px;
  font-weight: 700;
  color: var(--accent);
}
.st-spec-item-text {
  font-size: 12.5px;
  color: var(--text-secondary);
  line-height: 1.5;
}

/* ══ INTERACTIVE COLLAPSIBLE FAQ ACCORDION ══ */
.st-faq-grid {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin-top: 16px;
}
.st-accordion-item {
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  background: #ffffff;
  overflow: hidden;
  transition: border-color 0.2s ease;
}
.st-accordion-item:hover {
  border-color: var(--text-tertiary);
}
.st-accordion-header {
  padding: 16px 18px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  cursor: pointer;
  user-select: none;
  font-size: 14.5px;
  font-weight: 700;
  color: var(--text-primary);
  letter-spacing: -0.2px;
  background: #ffffff;
  transition: background 0.15s ease;
  min-height: 52px;
}
.st-accordion-header:hover {
  background: #fafafa;
}
.st-accordion-icon {
  width: 18px;
  height: 18px;
  color: var(--text-secondary);
  transition: transform 0.25s cubic-bezier(0.16, 1, 0.3, 1);
  flex-shrink: 0;
  margin-left: 12px;
}
.st-accordion-item.open .st-accordion-icon {
  transform: rotate(180deg);
  color: var(--accent);
}
.st-accordion-content {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.3s cubic-bezier(0.16, 1, 0.3, 1), padding 0.3s ease;
  padding: 0 18px;
  font-size: 13.5px;
  color: var(--text-secondary);
  line-height: 1.65;
}
.st-accordion-item.open .st-accordion-content {
  max-height: 400px;
  padding: 0 18px 18px;
}

/* ══ FOOTER (RESPONSIVE) ══ */
.st-footer {
  border-top: 1px solid var(--border-light);
  padding: 32px 20px;
  text-align: center;
  font-size: 13px;
  color: var(--text-secondary);
  background: #ffffff;
  margin-top: 60px;
}