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

:root {
  --primary-color: #1e40af;
  --primary-light: #3b82f6;
  --primary-dark: #1e3a8a;
  --secondary-color: #64748b;
  --bg-color: #f8fafc;
  --card-bg: #ffffff;
  --text-primary: #0f172a;
  --text-secondary: #64748b;
  --border-color: #e2e8f0;
  --success-color: #10b981;
  --danger-color: #ef4444;
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen', 'Ubuntu', 'Cantarell', sans-serif;
  background: var(--bg-color);
  min-height: 100vh;
  color: var(--text-primary);
}

.header {
  background: linear-gradient(135deg, #1e40af 0%, #3b82f6 100%);
  padding: 32px 24px 48px;
  color: white;
  box-shadow: var(--shadow-md);
}

.header-content {
  max-width: 560px;
  margin: 0 auto;
}

.header-top {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 20px;
}

.header h1 {
  font-size: 28px;
  font-weight: 700;
  letter-spacing: -0.5px;
}

.back-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  color: rgba(255, 255, 255, 0.9);
  text-decoration: none;
  font-size: 14px;
  padding: 8px 16px;
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.1);
  transition: all 0.2s ease;
}

.back-link:hover {
  background: rgba(255, 255, 255, 0.2);
  color: white;
}

.header p {
  font-size: 15px;
  opacity: 0.9;
}

.container {
  max-width: 560px;
  margin: -24px auto 40px;
  padding: 0 24px;
}

.card {
  background: var(--card-bg);
  border-radius: 16px;
  padding: 32px;
  box-shadow: var(--shadow-lg);
  border: 1px solid var(--border-color);
}

.tabs {
  display: flex;
  gap: 8px;
  margin-bottom: 32px;
  background: var(--bg-color);
  padding: 6px;
  border-radius: 12px;
}

.tab-btn {
  flex: 1;
  padding: 12px 16px;
  border: none;
  background: transparent;
  cursor: pointer;
  font-size: 15px;
  font-weight: 600;
  color: var(--text-secondary);
  border-radius: 8px;
  transition: all 0.2s ease;
}

.tab-btn:hover {
  color: var(--text-primary);
}

.tab-btn.active {
  background: var(--card-bg);
  color: var(--primary-color);
  box-shadow: var(--shadow-sm);
}

.form-group {
  margin-bottom: 24px;
}

.form-group label {
  display: block;
  margin-bottom: 8px;
  color: var(--text-primary);
  font-weight: 500;
  font-size: 14px;
}

.form-group input {
  width: 100%;
  padding: 12px 16px;
  border: 1px solid var(--border-color);
  border-radius: 8px;
  font-size: 15px;
  transition: all 0.2s ease;
  background: var(--card-bg);
}

.form-group input:focus {
  outline: none;
  border-color: var(--primary-light);
  box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
}

.code-input {
  display: flex;
  gap: 12px;
}

.code-input input {
  flex: 1;
}

.btn {
  padding: 12px 24px;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  font-size: 15px;
  font-weight: 600;
  transition: all 0.2s ease;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
}

.btn.primary {
  background: var(--primary-color);
  color: white;
  width: 100%;
}

.btn.primary:hover {
  background: var(--primary-dark);
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
}

.btn.primary:disabled {
  background: var(--secondary-color);
  cursor: not-allowed;
  transform: none;
}

.btn.secondary {
  background: var(--card-bg);
  color: var(--text-secondary);
  border: 1px solid var(--border-color);
  white-space: nowrap;
}

.btn.secondary:hover {
  background: var(--bg-color);
  border-color: var(--primary-light);
  color: var(--primary-color);
}

.btn.secondary:disabled {
  opacity: 0.6;
  cursor: not-allowed;
}

.invite-input {
  display: flex;
  gap: 12px;
}

.invite-input input {
  flex: 1;
}

.packages {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 16px;
  margin-bottom: 32px;
}

.package {
  border: 2px solid var(--border-color);
  border-radius: 12px;
  padding: 20px;
  cursor: pointer;
  text-align: center;
  transition: all 0.2s ease;
  background: var(--card-bg);
}

.package:hover {
  border-color: var(--primary-light);
  background: #eff6ff;
}

.package.selected {
  border-color: var(--primary-color);
  background: #eff6ff;
  box-shadow: 0 0 0 2px rgba(30, 64, 175, 0.1);
}

.package .amount {
  font-size: 32px;
  font-weight: 800;
  color: var(--primary-color);
  margin-bottom: 8px;
}

.package .price {
  color: var(--text-secondary);
  font-size: 14px;
}

.package .bonus {
  color: var(--success-color);
  font-size: 13px;
  margin-top: 8px;
  font-weight: 600;
}

.qr-code {
  text-align: center;
  padding: 32px 24px;
}

.qr-code img {
  width: 220px;
  height: 220px;
  border-radius: 12px;
  box-shadow: var(--shadow-md);
}

.qr-code p {
  margin-top: 20px;
  color: var(--text-secondary);
  font-size: 14px;
}

.qr-code .amount-display {
  font-size: 32px;
  font-weight: 800;
  color: var(--primary-color);
  margin: 16px 0;
}

.hidden {
  display: none !important;
}

.btn-group {
  display: flex;
  gap: 12px;
  margin-top: 12px;
}

.btn-group .btn {
  flex: 1;
}

@media (max-width: 768px) {
  .header {
    padding: 24px 16px 40px;
  }

  .header h1 {
    font-size: 24px;
  }

  .container {
    padding: 0 16px;
    margin-top: -20px;
  }

  .card {
    padding: 24px;
  }

  .packages {
    gap: 12px;
  }

  .package {
    padding: 16px;
  }

  .package .amount {
    font-size: 24px;
  }

  .qr-code img {
    width: 180px;
    height: 180px;
  }
}