:root {
  --ink: #0F1218;
  --cyan: #00E5FF;
  --cyan-50: #E8FCFF;
  --white: #FFFFFF;
  --gray-500: #5B6573;
  --gray-100: #F2F4F7;
  --blue: #4A90D9;
  --blue-light: #E8F4FD;
  --blue-dark: #2C6FAC;
  --shadow: 0 2px 12px rgba(0,0,0,0.08);
  --shadow-hover: 0 4px 20px rgba(0,0,0,0.12);
}

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

html {
  scroll-behavior: smooth;
}

body {
  font: 17px/1.6 -apple-system, BlinkMacSystemFont, "Segoe UI", Inter, system-ui, sans-serif;
  color: var(--ink);
  background: var(--white);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

.container {
  max-width: 1140px;
  margin: 0 auto;
  padding: 0 24px;
}

/* Header & Navigation */
header {
  background: var(--white);
  box-shadow: 0 1px 4px rgba(0,0,0,0.06);
  position: sticky;
  top: 0;
  z-index: 100;
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 24px;
  max-width: 1140px;
  margin: 0 auto;
}

.logo {
  font-size: 22px;
  font-weight: 800;
  color: var(--ink);
  text-decoration: none;
  display: flex;
  align-items: center;
  gap: 8px;
}

.logo span {
  color: var(--blue);
}

.nav-list {
  display: flex;
  list-style: none;
  gap: 4px;
}

.nav-list a {
  text-decoration: none;
  color: var(--gray-500);
  font-size: 15px;
  font-weight: 500;
  padding: 8px 14px;
  border-radius: 8px;
  transition: all 0.2s;
}

.nav-list a:hover,
.nav-list a.active {
  color: var(--ink);
  background: var(--gray-100);
}

.menu-toggle {
  display: none;
  background: none;
  border: none;
  font-size: 28px;
  cursor: pointer;
  color: var(--ink);
  padding: 4px;
}

/* Footer */
footer {
  background: var(--ink);
  color: var(--gray-500);
  text-align: center;
  padding: 32px 24px;
  margin-top: auto;
  font-size: 14px;
}

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

/* Hero Section */
.hero {
  background: linear-gradient(135deg, var(--ink) 0%, #1a2332 100%);
  color: var(--white);
  padding: 100px 24px;
  text-align: center;
}

.hero h1 {
  font-size: 56px;
  font-weight: 800;
  line-height: 1.05;
  margin-bottom: 16px;
}

.hero h1 span {
  color: var(--cyan);
}

.hero p {
  font-size: 20px;
  color: #9aa3b2;
  max-width: 600px;
  margin: 0 auto 32px;
}

.hero .btn {
  font-size: 18px;
  padding: 16px 36px;
}

/* Buttons */
.btn {
  display: inline-block;
  background: var(--cyan);
  color: var(--ink);
  padding: 14px 28px;
  border-radius: 8px;
  font-weight: 700;
  text-decoration: none;
  transition: all 0.25s;
  border: none;
  cursor: pointer;
  font-size: 16px;
}

.btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 14px rgba(0, 229, 255, 0.4);
}

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

.btn-primary:hover {
  background: var(--blue-dark);
  box-shadow: 0 4px 14px rgba(74, 144, 217, 0.4);
}

.btn-outline {
  background: transparent;
  color: var(--white);
  border: 2px solid var(--white);
}

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

.btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
  transform: none;
}

/* Section */
.section {
  padding: 80px 24px;
}

.section-title {
  font-size: 36px;
  font-weight: 700;
  text-align: center;
  margin-bottom: 12px;
}

.section-subtitle {
  font-size: 18px;
  color: var(--gray-500);
  text-align: center;
  margin-bottom: 48px;
  max-width: 600px;
  margin-left: auto;
  margin-right: auto;
}

/* Cards */
.cards-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 24px;
}

.card {
  background: var(--white);
  border: 1px solid var(--gray-100);
  border-radius: 16px;
  padding: 32px;
  transition: all 0.25s;
  box-shadow: var(--shadow);
}

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

.card-icon {
  font-size: 36px;
  margin-bottom: 16px;
}

.card h3 {
  font-size: 22px;
  font-weight: 700;
  margin-bottom: 12px;
}

.card p {
  color: var(--gray-500);
  margin-bottom: 20px;
}

.card .btn {
  font-size: 14px;
  padding: 10px 20px;
}

/* How it works */
.how-it-works {
  background: var(--gray-100);
}

.steps {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 32px;
  text-align: center;
}

.step-number {
  width: 48px;
  height: 48px;
  background: var(--cyan);
  color: var(--ink);
  font-size: 22px;
  font-weight: 800;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 0 auto 16px;
}

.step h3 {
  font-size: 20px;
  font-weight: 700;
  margin-bottom: 8px;
}

.step p {
  color: var(--gray-500);
  font-size: 15px;
}

/* Vocabulary page */
.vocab-table {
  width: 100%;
  border-collapse: collapse;
  background: var(--white);
  border-radius: 12px;
  overflow: hidden;
  box-shadow: var(--shadow);
}

.vocab-table th {
  background: var(--blue);
  color: var(--white);
  padding: 14px 18px;
  text-align: left;
  font-weight: 600;
}

.vocab-table td {
  padding: 12px 18px;
  border-bottom: 1px solid var(--gray-100);
}

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

.vocab-table tr:hover td {
  background: var(--blue-light);
}

.vocab-categories {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  justify-content: center;
  margin-bottom: 32px;
}

.category-btn {
  padding: 8px 18px;
  border-radius: 20px;
  border: 2px solid var(--gray-100);
  background: var(--white);
  cursor: pointer;
  font-size: 14px;
  font-weight: 500;
  transition: all 0.2s;
}

.category-btn:hover,
.category-btn.active {
  background: var(--blue);
  color: var(--white);
  border-color: var(--blue);
}

/* Grammar page */
.grammar-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 24px;
}

.grammar-card {
  background: var(--white);
  border: 1px solid var(--gray-100);
  border-radius: 16px;
  padding: 28px;
  box-shadow: var(--shadow);
}

.grammar-card h3 {
  font-size: 22px;
  font-weight: 700;
  margin-bottom: 12px;
  color: var(--blue);
}

.grammar-card .formula {
  background: var(--cyan-50);
  padding: 12px 16px;
  border-radius: 8px;
  font-family: monospace;
  font-size: 16px;
  margin: 12px 0;
  border-left: 3px solid var(--cyan);
}

.grammar-card .examples {
  margin-top: 12px;
}

.grammar-card .examples li {
  list-style: none;
  padding: 6px 0;
  color: var(--gray-500);
}

.grammar-card .examples li::before {
  content: "→ ";
  color: var(--blue);
  font-weight: 700;
}

/* Exercises page */
.exercise {
  background: var(--white);
  border: 1px solid var(--gray-100);
  border-radius: 16px;
  padding: 28px;
  margin-bottom: 24px;
  box-shadow: var(--shadow);
}

.exercise h3 {
  font-size: 18px;
  font-weight: 700;
  margin-bottom: 16px;
}

.exercise .question {
  font-size: 17px;
  margin-bottom: 16px;
}

.exercise .options {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.exercise .option {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 10px 16px;
  border: 2px solid var(--gray-100);
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.2s;
}

.exercise .option:hover {
  border-color: var(--blue);
  background: var(--blue-light);
}

.exercise .option input[type="radio"] {
  accent-color: var(--blue);
  width: 18px;
  height: 18px;
}

.exercise .option.correct {
  border-color: #28a745;
  background: #e8f5e9;
}

.exercise .option.wrong {
  border-color: #dc3545;
  background: #fce4ec;
}

.exercise .feedback {
  margin-top: 12px;
  padding: 10px 16px;
  border-radius: 8px;
  font-weight: 600;
  display: none;
}

.exercise .feedback.correct {
  display: block;
  background: #e8f5e9;
  color: #28a745;
}

.exercise .feedback.wrong {
  display: block;
  background: #fce4ec;
  color: #dc3545;
}

.fill-input {
  padding: 8px 12px;
  border: 2px solid var(--gray-100);
  border-radius: 8px;
  font-size: 16px;
  width: 200px;
  transition: border-color 0.2s;
}

.fill-input:focus {
  outline: none;
  border-color: var(--blue);
}

.fill-input.correct {
  border-color: #28a745;
  background: #e8f5e9;
}

.fill-input.wrong {
  border-color: #dc3545;
  background: #fce4ec;
}

/* Tests page */
.test-question {
  background: var(--white);
  border: 1px solid var(--gray-100);
  border-radius: 16px;
  padding: 24px;
  margin-bottom: 16px;
  box-shadow: var(--shadow);
}

.test-question h4 {
  font-size: 16px;
  font-weight: 600;
  margin-bottom: 12px;
}

.test-question .options {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.test-question .option {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 8px 14px;
  border: 2px solid var(--gray-100);
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.2s;
}

.test-question .option:hover {
  border-color: var(--blue);
}

.test-question .option input[type="radio"] {
  accent-color: var(--blue);
}

.result-box {
  text-align: center;
  padding: 32px;
  background: var(--blue-light);
  border-radius: 16px;
  margin-top: 24px;
  display: none;
}

.result-box.show {
  display: block;
}

.result-box .score {
  font-size: 48px;
  font-weight: 800;
  color: var(--blue);
}

.result-box p {
  font-size: 18px;
  color: var(--gray-500);
  margin-top: 8px;
}

/* Reading page */
.reading-text {
  background: var(--white);
  border: 1px solid var(--gray-100);
  border-radius: 16px;
  padding: 28px;
  margin-bottom: 24px;
  box-shadow: var(--shadow);
}

.reading-text h3 {
  font-size: 22px;
  font-weight: 700;
  margin-bottom: 16px;
  color: var(--blue);
}

.reading-text .text-content {
  line-height: 1.8;
  margin-bottom: 20px;
  font-size: 16px;
}

.reading-text .questions h4 {
  font-weight: 600;
  margin-bottom: 12px;
  font-size: 16px;
}

.reading-text .questions ol {
  margin-left: 20px;
}

.reading-text .questions li {
  margin-bottom: 8px;
  color: var(--gray-500);
}

/* Contact page */
.contact-form {
  max-width: 600px;
  margin: 0 auto;
  background: var(--white);
  border: 1px solid var(--gray-100);
  border-radius: 16px;
  padding: 40px;
  box-shadow: var(--shadow);
}

.form-group {
  margin-bottom: 20px;
}

.form-group label {
  display: block;
  font-weight: 600;
  margin-bottom: 6px;
  font-size: 15px;
}

.form-group input,
.form-group textarea {
  width: 100%;
  padding: 12px 16px;
  border: 2px solid var(--gray-100);
  border-radius: 8px;
  font-size: 16px;
  font-family: inherit;
  transition: border-color 0.2s;
}

.form-group input:focus,
.form-group textarea:focus {
  outline: none;
  border-color: var(--blue);
}

.form-group textarea {
  min-height: 120px;
  resize: vertical;
}

.contact-form .btn {
  width: 100%;
}

.form-message {
  text-align: center;
  padding: 20px;
  background: #e8f5e9;
  color: #28a745;
  border-radius: 12px;
  margin-top: 16px;
  font-weight: 600;
  display: none;
}

.form-message.show {
  display: block;
}

/* Page header */
.page-header {
  background: linear-gradient(135deg, var(--blue) 0%, var(--blue-dark) 100%);
  color: var(--white);
  padding: 60px 24px;
  text-align: center;
}

.page-header h1 {
  font-size: 42px;
  font-weight: 800;
  margin-bottom: 8px;
}

.page-header p {
  font-size: 18px;
  opacity: 0.9;
}

/* Mobile */
@media (max-width: 768px) {
  .menu-toggle {
    display: block;
  }

  .nav-list {
    display: none;
    flex-direction: column;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: var(--white);
    box-shadow: 0 4px 12px rgba(0,0,0,0.1);
    padding: 8px;
    gap: 2px;
  }

  .nav-list.open {
    display: flex;
  }

  .nav-list a {
    padding: 12px 16px;
    border-radius: 8px;
  }

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

  .hero p {
    font-size: 18px;
  }

  .section {
    padding: 48px 20px;
  }

  .section-title {
    font-size: 28px;
  }

  .page-header h1 {
    font-size: 32px;
  }

  .page-header {
    padding: 40px 20px;
  }

  .cards-grid {
    grid-template-columns: 1fr;
  }

  .grammar-grid {
    grid-template-columns: 1fr;
  }

  .steps {
    grid-template-columns: 1fr;
  }

  .vocab-table {
    font-size: 14px;
  }

  .vocab-table th,
  .vocab-table td {
    padding: 10px 12px;
  }

  .contact-form {
    padding: 24px;
  }

  .fill-input {
    width: 100%;
  }
}

@media (max-width: 480px) {
  .header-inner {
    padding: 10px 16px;
  }

  .logo {
    font-size: 18px;
  }

  .hero {
    padding: 60px 16px;
  }

  .hero h1 {
    font-size: 28px;
  }

  .card {
    padding: 24px;
  }
}