:root {
  --bg: #f0f0f0;
  --surface: #ffffff;
  --text: #2f3145;
  --text-soft: #4d4d5c;
  --primary: #1494d5;
  --primary-hover: #0f84c0;
  --border: #d9dee7;
  --shadow: 0 10px 30px rgba(47, 49, 69, 0.08);
  --radius: 16px;
  --container: 1180px;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
}

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

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

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

.container {
  width: min(var(--container), calc(100% - 32px));
  margin: 0 auto;
}

.site-header {
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  min-height: 80px;
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  min-height: 80px;
  gap: 20px;
  padding: 10px 0;
}

.logo-wrap img {
  height: 60px;
  width: auto;
}

.main-nav {
  display: flex;
  gap: 24px;
  flex-wrap: wrap;
  justify-content: flex-end;
  font-weight: bold;
}

.main-nav a {
  display: inline-flex;
  align-items: center;
  min-height: 40px;
}

.hero {
  padding: 48px 0 24px;
}

.hero-grid {
  display: grid;
  grid-template-columns: 1.2fr 0.8fr;
  gap: 24px;
  align-items: center;
}

.hero-text h1 {
  margin: 0 0 12px;
  font-size: 48px;
  line-height: 1.1;
}

.hero-text p {
  margin: 0 0 20px;
  color: var(--text-soft);
  font-size: 18px;
  max-width: 700px;
}

.hero-buttons {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 48px;
  padding: 12px 20px;
  border-radius: 12px;
  font-weight: bold;
  border: 1px solid transparent;
  text-align: center;
}

.btn-primary {
  background: var(--primary);
  color: white;
}

.btn-primary:hover {
  background: var(--primary-hover);
  color: white;
}

.btn-secondary {
  background: var(--surface);
  border-color: var(--border);
  color: var(--text);
}

.hero-card,
.section-card,
.calculator-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.hero-card {
  padding: 24px;
}

.hero-card h2 {
  margin-top: 0;
  margin-bottom: 10px;
  font-size: 24px;
}

.hero-card p {
  margin: 0;
  color: var(--text-soft);
}

.main-content {
  padding: 12px 0 60px;
}

.content-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 320px;
  gap: 24px;
  align-items: start;
}

.calculator-card {
  padding: 24px;
  margin-bottom: 24px;
}

.calculator-card h2 {
  margin-top: 0;
  margin-bottom: 8px;
  font-size: 30px;
}

.calculator-card p {
  margin-top: 0;
  color: var(--text-soft);
}

.form-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  margin: 20px 0;
}

.field label {
  display: block;
  margin-bottom: 8px;
  font-weight: bold;
}

.field input,
.field select {
  width: 100%;
  min-height: 52px;
  padding: 0 14px;
  border: 1px solid var(--border);
  border-radius: 12px;
  font-size: 16px;
  background: white;
  color: var(--text);
}

.field input:focus,
.field select:focus {
  outline: 2px solid rgba(20, 148, 213, 0.2);
  border-color: var(--primary);
}

.button-row {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  margin-bottom: 20px;
}

.calc-btn {
  min-height: 50px;
  padding: 0 18px;
  border: none;
  border-radius: 12px;
  font-size: 16px;
  font-weight: bold;
  cursor: pointer;
  text-align: center;
}

.calc-btn-primary {
  background: var(--primary);
  color: white;
}

.calc-btn-primary:hover {
  background: var(--primary-hover);
}

.calc-btn-secondary {
  background: #eef5fa;
  color: var(--text);
}

.result-box {
  padding: 18px;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: #f7fbfe;
  overflow: hidden;
}

.result-label {
  display: block;
  margin-bottom: 8px;
  font-size: 14px;
  color: var(--text-soft);
  font-weight: bold;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.result-value {
  font-size: 30px;
  font-weight: bold;
  color: var(--primary);
  word-break: break-word;
  overflow-wrap: anywhere;
  line-height: 1.25;
}

.section-card {
  padding: 24px;
  margin-bottom: 24px;
}

.section-card h2 {
  margin-top: 0;
  font-size: 28px;
}

.section-card h3 {
  margin-bottom: 8px;
}

.section-card p,
.section-card li {
  color: var(--text-soft);
}

.formula-box,
.example-box {
  background: #f8fbff;
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 16px;
}

.related-links {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}

.related-links a {
  display: block;
  padding: 14px;
  border: 1px solid var(--border);
  border-radius: 12px;
  background: #f8fbff;
  font-weight: bold;
}

.sidebar {
  display: flex;
  flex-direction: column;
  gap: 24px;
  position: sticky;
  top: 20px;
}

.sidebar-card,
.ad-banner,
.ad-box,
.formula-box,
.example-box,
.link-card,
.related-links a {
  overflow-wrap: anywhere;
}

.sidebar-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 20px;
}

.sidebar-card h3 {
  margin-top: 0;
  font-size: 22px;
}

.toc {
  margin: 0;
  padding-left: 18px;
}

.toc li {
  margin-bottom: 10px;
}

.ad-box {
  min-height: 250px;
  display: grid;
  place-items: center;
  border: 2px dashed #c7d8e5;
  border-radius: 14px;
  background: #f8fbff;
  color: var(--text-soft);
  text-align: center;
  font-weight: bold;
  padding: 20px;
}

.site-footer {
  background: var(--surface);
  border-top: 1px solid var(--border);
  padding: 30px 0;
}

.footer-links {
  display: flex;
  gap: 16px;
  flex-wrap: wrap;
  margin-top: 10px;
}

@media (max-width: 980px) {
  .hero-grid,
  .content-grid,
  .form-grid,
  .related-links {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: static;
    gap: 20px;
  }

  .sidebar-card {
    padding: 18px;
  }
}

@media (max-width: 720px) {
  .site-header {
    min-height: 0;
  }

  .header-inner {
    flex-direction: column;
    align-items: stretch;
    gap: 12px;
    padding: 14px 0;
  }

  .main-nav {
    gap: 10px;
    justify-content: flex-start;
  }

  .main-nav a {
    min-height: 36px;
    padding: 6px 10px;
    border: 1px solid var(--border);
    border-radius: 10px;
    background: #f8fbff;
  }

  .hero {
    padding: 32px 0 20px;
  }

  .hero-text h1 {
    font-size: 36px;
  }

  .hero-text p {
    font-size: 16px;
  }

  .logo-wrap img {
    height: 64px;
  }

  .hero-card,
  .section-card,
  .calculator-card {
    padding: 20px;
  }

  .calculator-card h2,
  .section-card h2 {
    font-size: 26px;
  }

  .button-row,
  .hero-buttons {
    flex-direction: column;
  }

  .calc-btn,
  .btn {
    width: 100%;
  }

  .ad-box {
    min-height: 140px;
    padding: 18px;
  }

  .ad-banner .ad-box {
    min-height: 100px;
  }

  .calc-shell {
    max-width: 100%;
    padding: 18px 14px 14px;
  }

  .calc-screen {
    min-height: 72px;
    padding: 0 12px;
    font-size: 1.7rem;
    overflow-x: auto;
  }

  .calc-keys {
    gap: 10px;
  }

  .calc-key {
    min-height: 52px;
    font-size: 1.2rem;
  }
}

@media (max-width: 520px) {
  .container {
    width: min(var(--container), calc(100% - 24px));
  }

  .hero-text h1 {
    font-size: 30px;
  }

  .calculator-card,
  .section-card,
  .hero-card,
  .sidebar-card {
    padding: 16px;
  }

  .calculator-card h2,
  .section-card h2,
  .hero-card h2,
  .sidebar-card h3 {
    font-size: 22px;
  }

  .related-links a,
  .link-card {
    padding: 14px;
  }

  .result-box {
    padding: 16px;
  }

  .result-value {
    font-size: 24px;
  }

  .calc-screen {
    font-size: 1.45rem;
  }
}

.calculator-hero {
  padding: 28px;
  display: flex;
  justify-content: center;
}

.calc-shell {
  width: 100%;
  max-width: 360px;
  background: #fcfcfd;
  border: 4px solid #2f3145;
  border-radius: 28px;
  padding: 22px 18px 18px;
  position: relative;
}

.calc-top-accent {
  width: 64px;
  height: 16px;
  background: #1494d5;
  border-radius: 6px;
  margin-left: auto;
  margin-bottom: 18px;
}

.calc-screen {
  min-height: 84px;
  border: 4px solid #1494d5;
  border-radius: 10px;
  background: #f3f5f7;
  color: #2f3145;
  font-size: 2rem;
  font-weight: bold;
  display: flex;
  align-items: center;
  justify-content: flex-end;
  padding: 0 16px;
  margin-bottom: 18px;
  overflow: hidden;
}

.calc-keys {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
}

.calc-key {
  min-height: 58px;
  border: 4px solid #2f3145;
  border-radius: 14px;
  background: #ffffff;
  color: #2f3145;
  font-size: 1.4rem;
  font-weight: bold;
  cursor: pointer;
  transition: transform 0.08s ease, background 0.15s ease;
}

.calc-key:hover {
  background: #f6f9fc;
}

.calc-key:active {
  transform: translateY(1px);
}

.calc-key-accent {
  border-color: #1494d5;
  color: #1494d5;
}

.calc-key-light {
  border-color: #1494d5;
  color: #1494d5;
  background: #f7fbfe;
}

.calc-key-zero {
  grid-column: span 2;
}

/* --- Discovery / category pages --- */

.card-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  margin: 16px 0;
}

.link-card {
  display: block;
  padding: 18px;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: #f8fbff;
  transition: border-color 0.15s ease, box-shadow 0.15s ease;
}

.link-card h3 {
  margin: 0 0 6px;
  font-size: 18px;
  color: var(--text);
}

.link-card p {
  margin: 0;
  font-size: 14px;
  color: var(--text-soft);
}

.link-card:hover {
  border-color: var(--primary);
  box-shadow: 0 4px 12px rgba(20, 148, 213, 0.1);
  color: var(--text);
}

.link-card-muted {
  opacity: 0.6;
  cursor: default;
}

.ad-banner {
  margin-bottom: 24px;
}

.ad-banner .ad-box {
  min-height: 90px;
}

.category-more {
  margin-top: 12px;
  margin-bottom: 0;
  font-weight: bold;
}

.category-more a {
  color: var(--primary);
}

@media (max-width: 980px) {
  .card-grid {
    grid-template-columns: 1fr;
  }
}
@media (max-width: 980px) {
  .hero-grid,
  .content-grid,
  .form-grid,
  .related-links {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: static;
    gap: 20px;
  }

  .sidebar-card {
    padding: 18px;
  }
}

@media (max-width: 720px) {
  .site-header {
    min-height: 0;
  }

  .header-inner {
    flex-direction: column;
    align-items: stretch;
    gap: 12px;
    padding: 14px 0;
  }

  .main-nav {
    gap: 10px;
    justify-content: flex-start;
  }

  .main-nav a {
    min-height: 36px;
    padding: 6px 10px;
    border: 1px solid var(--border);
    border-radius: 10px;
    background: #f8fbff;
  }

  .hero {
    padding: 32px 0 20px;
  }

  .hero-text h1 {
    font-size: 36px;
  }

  .hero-text p {
    font-size: 16px;
  }

  .logo-wrap img {
    height: 64px;
  }

  .hero-card,
  .section-card,
  .calculator-card {
    padding: 20px;
  }

  .calculator-card h2,
  .section-card h2 {
    font-size: 26px;
  }

  .button-row,
  .hero-buttons {
    flex-direction: column;
  }

  .calc-btn,
  .btn {
    width: 100%;
  }

  .ad-box {
    min-height: 140px;
    padding: 18px;
  }

  .ad-banner .ad-box {
    min-height: 100px;
  }

  .calc-shell {
    max-width: 100%;
    padding: 18px 14px 14px;
  }

  .calc-screen {
    min-height: 72px;
    padding: 0 12px;
    font-size: 1.7rem;
    overflow-x: auto;
  }

  .calc-keys {
    gap: 10px;
  }

  .calc-key {
    min-height: 52px;
    font-size: 1.2rem;
  }
}

@media (max-width: 520px) {
  .container {
    width: min(var(--container), calc(100% - 24px));
  }

  .hero-text h1 {
    font-size: 30px;
  }

  .calculator-card,
  .section-card,
  .hero-card,
  .sidebar-card {
    padding: 16px;
  }

  .calculator-card h2,
  .section-card h2,
  .hero-card h2,
  .sidebar-card h3 {
    font-size: 22px;
  }

  .related-links a,
  .link-card {
    padding: 14px;
  }

  .result-box {
    padding: 16px;
  }

  .result-value {
    font-size: 24px;
  }

  .calc-screen {
    font-size: 1.45rem;
  }
}