:root {
  /* Color Palette */
  --bg-navy-deep: #001233;
  --bg-navy-royal: #002366;
  --color-gold: #FFD700;
  --color-safety-orange: #FF6700;
  --color-text-primary: #F0F4F8;
  --color-text-secondary: #94A3B8;
  --color-accent: #38BDF8; /* Sky blue for subtle links */
  
  /* Typography */
  --font-main: 'Inter', system-ui, -apple-system, sans-serif;
  --font-tech: 'JetBrains Mono', monospace;
  
  /* Spacing */
  --spacing-xs: 0.5rem;
  --spacing-sm: 1rem;
  --spacing-md: 2rem;
  --spacing-lg: 4rem;
}

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

body {
  font-family: var(--font-main);
  background-color: var(--bg-navy-deep);
  color: var(--color-text-primary);
  line-height: 1.6;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
}

/* --- Layout --- */

header {
  background: rgba(0, 35, 102, 0.8);
  backdrop-filter: blur(12px);
  padding: var(--spacing-sm) var(--spacing-md);
  position: fixed;
  width: 100%;
  top: 0;
  z-index: 1000;
  border-bottom: 1px solid rgba(255, 215, 0, 0.1);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.logo {
  font-weight: 800;
  font-size: 1.5rem;
  color: var(--color-gold);
  text-transform: uppercase;
  letter-spacing: 2px;
}

nav ul {
  display: flex;
  list-style: none;
  gap: var(--spacing-md);
}

nav a {
  text-decoration: none;
  color: var(--color-text-secondary);
  font-weight: 500;
  transition: color 0.3s ease;
  font-size: 0.9rem;
}

nav a:hover {
  color: var(--color-gold);
}

/* --- Hero Section --- */

.hero {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  text-align: center;
  padding: var(--spacing-lg) var(--spacing-md);
  background: radial-gradient(circle at center, var(--bg-navy-royal) 0%, var(--bg-navy-deep) 100%);
}

.hero h1 {
  font-size: clamp(2.5rem, 8vw, 4.5rem);
  font-weight: 900;
  margin-bottom: var(--spacing-sm);
  background: linear-gradient(to bottom, #FFFFFF, var(--color-gold));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.hero p {
  font-size: 1.25rem;
  color: var(--color-text-secondary);
  max-width: 700px;
  margin-bottom: var(--spacing-md);
}

.btn-primary {
  background: var(--color-gold);
  color: var(--bg-navy-deep);
  padding: 0.8rem 2rem;
  border-radius: 4px;
  font-weight: 700;
  text-decoration: none;
  transition: transform 0.2s ease, box-shadow 0.2s ease;
  display: inline-block;
  box-shadow: 0 4px 15px rgba(255, 215, 0, 0.3);
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(255, 215, 0, 0.4);
}

/* --- Interactive Elements --- */

.calculator-section {
  padding: var(--spacing-lg) var(--spacing-md);
  background: var(--bg-navy-deep);
}

.card {
  background: linear-gradient(145deg, var(--bg-navy-royal), #001a4d);
  border: 1px solid rgba(255, 215, 0, 0.05);
  padding: var(--spacing-md);
  border-radius: 12px;
  box-shadow: 0 10px 30px rgba(0,0,0,0.4);
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.card:hover {
  border-color: var(--color-gold);
  transform: translateY(-5px);
  box-shadow: 0 15px 40px rgba(0,0,0,0.6), 0 0 20px rgba(255, 215, 0, 0.1);
}

input, select {
  outline: none;
  transition: border-color 0.2s;
}

input:focus, select:focus {
  border-color: var(--color-safety-orange) !important;
  box-shadow: 0 0 10px rgba(255, 103, 0, 0.2);
}

/* --- Mobile First Responsiveness --- */

@media (max-width: 900px) {
  header {
    padding: var(--spacing-sm);
  }

  nav {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    width: 100%;
    background: var(--bg-navy-royal);
    padding: var(--spacing-md);
    border-bottom: 2px solid var(--color-gold);
  }

  nav.active {
    display: block;
  }

  nav ul {
    flex-direction: column;
    gap: var(--spacing-sm);
    text-align: center;
  }

  #mobile-menu-btn {
    display: block !important;
  }

  .hero h1 {
    font-size: 2.8rem;
  }
}

/* --- Technical Details --- */

.tech-tag {
  font-family: var(--font-tech);
  color: var(--color-safety-orange);
  font-size: 0.8rem;
  background: rgba(255, 103, 0, 0.1);
  padding: 2px 8px;
  border-radius: 4px;
  text-transform: uppercase;
}