/* =========================================================================
   DESIGN SYSTEM & GLOBAL STYLES (main.css)
   HK Filtration — Corporate B2B Industrial Theme
   ========================================================================= */

/* --- Google Fonts --- */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800&display=swap');

/* --- Design System CSS Custom Properties --- */
:root {
  /* Fonts */
  --font-body: 'Inter', system-ui, -apple-system, sans-serif;
  --font-headings: 'Inter', system-ui, -apple-system, sans-serif;
  
  /* Color Palette - Clean Corporate */
  --primary: #1a365d;          /* Deep Navy */
  --primary-hover: #2d4a7c;
  --primary-light: #edf2f7;
  --primary-semi: rgba(26, 54, 93, 0.1);
  
  --accent: #c53030;           /* Professional Red */
  --accent-hover: #9b2c2c;
  --accent-light: #fff5f5;
  
  --bg-primary: #ffffff;
  --bg-secondary: #f7f8fa;
  --bg-tertiary: #edf2f7;
  
  --text-primary: #1a202c;
  --text-secondary: #4a5568;
  --text-muted: #a0aec0;
  
  --border-color: #e2e8f0;
  --border-focus: var(--primary);
  
  --shadow-sm: 0 1px 3px 0 rgb(0 0 0 / 0.06), 0 1px 2px -1px rgb(0 0 0 / 0.06);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.07), 0 2px 4px -2px rgb(0 0 0 / 0.05);
  --shadow-lg: 0 10px 25px -5px rgb(0 0 0 / 0.08), 0 8px 10px -6px rgb(0 0 0 / 0.04);
  --shadow-xl: 0 20px 40px -10px rgb(0 0 0 / 0.1);

  /* Spacing / Layout */
  --header-height: 72px;
  --radius: 6px;
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --container-width: 1240px;
  
  /* Transitions */
  --transition-fast: 0.15s ease;
  --transition-normal: 0.25s ease;
  --transition-slow: 0.4s ease;
}

/* --- Base & Reset CSS --- */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-body);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.65;
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-headings);
  font-weight: 700;
  line-height: 1.25;
  color: var(--text-primary);
  letter-spacing: -0.01em;
}

h1 { font-size: 2.75rem; }
h2 { font-size: 2rem; }
h3 { font-size: 1.5rem; }
h4 { font-size: 1.125rem; }

p {
  color: var(--text-secondary);
  margin-bottom: 1rem;
}

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

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

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

ul, ol {
  list-style: none;
}

/* --- Layout Utilities --- */
.container {
  width: 100%;
  max-width: var(--container-width);
  margin: 0 auto;
  padding: 0 1.5rem;
}

.section-padding {
  padding: 5rem 0;
}

.grid {
  display: grid;
  gap: 2rem;
}

.grid-2 {
  grid-template-columns: repeat(2, 1fr);
}

.grid-3 {
  grid-template-columns: repeat(3, 1fr);
}

.grid-4 {
  grid-template-columns: repeat(4, 1fr);
}

.flex {
  display: flex;
}

.flex-column {
  flex-direction: column;
}

.flex-align-center {
  align-items: center;
}

.gap-1 { gap: 0.5rem; }
.gap-2 { gap: 1rem; }
.gap-3 { gap: 1.5rem; }

.text-gradient {
  color: var(--primary);
}

/* Section Header */
.section-header {
  text-align: center;
  max-width: 640px;
  margin: 0 auto 3rem;
}

.section-header h2 {
  margin-bottom: 0.75rem;
}

.section-header p {
  font-size: 1.05rem;
}

.accent-title {
  position: relative;
  display: inline-block;
}

.accent-title::after {
  content: '';
  position: absolute;
  bottom: -8px;
  left: 0;
  width: 48px;
  height: 3px;
  background: var(--accent);
  border-radius: 2px;
}

.section-header .accent-title::after {
  left: 50%;
  transform: translateX(-50%);
}

/* --- Buttons --- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.7rem 1.75rem;
  font-family: var(--font-body);
  font-size: 0.9rem;
  font-weight: 600;
  border-radius: var(--radius);
  border: 2px solid transparent;
  cursor: pointer;
  transition: all var(--transition-fast);
  text-decoration: none;
  gap: 0.5rem;
  letter-spacing: 0.01em;
}

.btn-accent {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
}

.btn-accent:hover {
  background: var(--accent-hover);
  border-color: var(--accent-hover);
  color: #fff;
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
}

.btn-primary {
  background: var(--primary);
  color: #fff;
  border-color: var(--primary);
}

.btn-primary:hover {
  background: var(--primary-hover);
  border-color: var(--primary-hover);
  color: #fff;
  transform: translateY(-1px);
}

.btn-secondary {
  background: transparent;
  color: var(--primary);
  border-color: var(--primary);
}

.btn-secondary:hover {
  background: var(--primary);
  color: #fff;
  transform: translateY(-1px);
}

.btn-outline-primary {
  background: transparent;
  color: var(--primary);
  border-color: var(--border-color);
}

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

.hero-btns {
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
}

/* --- Responsive --- */
@media (max-width: 1024px) {
  .grid-4 { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 768px) {
  h1 { font-size: 2rem; }
  h2 { font-size: 1.5rem; }
  
  .grid-2,
  .grid-3,
  .grid-4 {
    grid-template-columns: 1fr;
  }
  
  .section-padding {
    padding: 3rem 0;
  }
  
  .hero-btns {
    flex-direction: column;
  }
  
  .btn {
    width: 100%;
    justify-content: center;
  }
}