/* ==========================================================
   MSportFit Landing — Stage 4: Styling & Responsiveness
   Mobile-first | System fonts | No external dependencies
   ========================================================== */

/* ===== CSS CUSTOM PROPERTIES ===== */
:root {
  --color-primary: #2563eb;
  --color-primary-light: #3b82f6;
  --color-secondary: #1e40af;
  --color-accent: #dbeafe;
  --color-text: #1f2937;
  --color-text-light: #6b7280;
  --color-bg: #ffffff;
  --color-bg-alt: #f1f5f9;
  --color-border: #e2e8f0;
  --color-surface: #ffffff;

  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
    "Helvetica Neue", Arial, sans-serif;
  --font-mono: ui-monospace, "Cascadia Code", "Courier New", monospace;

  --spacing-xs: 0.5rem;
  --spacing-sm: 1rem;
  --spacing-md: 1.5rem;
  --spacing-lg: 2rem;
  --spacing-xl: 3rem;
  --spacing-2xl: 4rem;
  --spacing-3xl: 6rem;

  --max-width: 1140px;
  --content-width: 720px;
  --border-radius: 0.5rem;
  --border-radius-lg: 0.75rem;
  --transition: 0.25s ease;

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.07),
    0 2px 4px -2px rgba(0, 0, 0, 0.05);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.08),
    0 4px 6px -4px rgba(0, 0, 0, 0.04);
}

/* ===== RESET ===== */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

/* ===== BASE TYPOGRAPHY (mobile-first) ===== */
body {
  font-family: var(--font-sans);
  font-size: 1rem;
  line-height: 1.7;
  color: var(--color-text);
  background-color: var(--color-bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

h1,
h2,
h3,
h4,
h5,
h6 {
  line-height: 1.25;
  font-weight: 700;
  margin-bottom: var(--spacing-sm);
  letter-spacing: -0.01em;
}

h1 {
  font-size: 1.75rem;
}
h2 {
  font-size: 1.5rem;
}
h3 {
  font-size: 1.25rem;
}

p {
  margin-bottom: var(--spacing-sm);
  max-width: 65ch;
  margin-left: auto;
  margin-right: auto;
}

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

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

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

/* ===== FOCUS VISIBLE (a11y) ===== */
a:focus-visible,
button:focus-visible {
  outline: 3px solid var(--color-primary);
  outline-offset: 2px;
  border-radius: 2px;
}

*:focus:not(:focus-visible) {
  outline: none;
}

/* ===== SKIP LINK (a11y) ===== */
.skip-link {
  position: absolute;
  top: -40px;
  left: 0;
  background-color: var(--color-primary);
  color: var(--color-bg);
  padding: var(--spacing-xs) var(--spacing-md);
  text-decoration: none;
  z-index: 100;
  border-radius: 0 0 var(--border-radius) 0;
  font-weight: 600;
}

.skip-link:focus {
  top: 0;
}

/* ===== CONTAINER ===== */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--spacing-sm);
}

/* ===== UTILITY CLASSES ===== */
.text-center {
  text-align: center;
}
.text-light {
  color: var(--color-text-light);
}
.mt-sm {
  margin-top: var(--spacing-sm);
}
.mt-md {
  margin-top: var(--spacing-md);
}
.mt-lg {
  margin-top: var(--spacing-lg);
}
.mb-sm {
  margin-bottom: var(--spacing-sm);
}
.mb-md {
  margin-bottom: var(--spacing-md);
}
.mb-lg {
  margin-bottom: var(--spacing-lg);
}

/* ===== HEADER ===== */
.header {
  border-bottom: 1px solid var(--color-border);
  padding: var(--spacing-sm) 0;
  position: sticky;
  top: 0;
  z-index: 50;
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
}

.header-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: var(--spacing-sm);
  flex-wrap: wrap;
}

.logo a {
  color: var(--color-text);
  font-size: 1.25rem;
  text-decoration: none;
  letter-spacing: -0.02em;
  display: flex;
  align-items: center;
  gap: var(--spacing-xs);
}

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

/* ===== LANGUAGE SWITCHER ===== */
.lang-switcher {
  display: flex;
  gap: 0.125rem;
  border: 1px solid var(--color-border);
  border-radius: var(--border-radius);
  padding: 0.1875rem;
  background: var(--color-bg-alt);
}

.lang-btn {
  padding: 0.375rem 0.75rem;
  border: none;
  background: transparent;
  color: var(--color-text);
  cursor: pointer;
  font-weight: 600;
  border-radius: calc(var(--border-radius) - 2px);
  transition: all var(--transition);
  font-family: var(--font-sans);
  font-size: 0.8125rem;
  letter-spacing: 0.05em;
  line-height: 1;
}

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

.lang-btn.active {
  background: var(--color-primary);
  color: white;
  box-shadow: var(--shadow-sm);
}

.lang-btn.active:hover {
  background: var(--color-secondary);
  color: white;
}

/* ===== HERO ===== */
.hero {
  background: linear-gradient(160deg, #dbeafe 0%, #eff6ff 50%, #f8fafc 100%);
  padding: var(--spacing-2xl) 0 var(--spacing-xl);
  text-align: center;
  border-bottom: 1px solid var(--color-border);
}

.hero-title {
  font-size: 1.75rem;
  margin-bottom: var(--spacing-sm);
  letter-spacing: -0.02em;
  color: var(--color-text);
  line-height: 1.2;
}

.hero-subtitle {
  font-size: 1.0625rem;
  color: var(--color-text-light);
  margin-bottom: var(--spacing-md);
  font-weight: 400;
  font-style: italic;
}

.hero-description {
  font-size: 1rem;
  line-height: 1.75;
  max-width: var(--content-width);
  margin: 0 auto var(--spacing-lg);
  color: var(--color-text);
}

/* ===== HERO KEYWORDS (chips) ===== */
.hero-keywords {
  max-width: var(--content-width);
  margin: 0 auto var(--spacing-xl);
}

.keywords-label {
  display: block;
  font-weight: 600;
  font-size: 0.8125rem;
  color: var(--color-text-light);
  margin-bottom: var(--spacing-xs);
  text-transform: uppercase;
  letter-spacing: 0.06em;
}

.chips {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  justify-content: center;
}

.chip {
  display: inline-block;
  padding: 0.3125rem 0.75rem;
  background: var(--color-accent);
  color: var(--color-secondary);
  border-radius: 100px;
  font-size: 0.8125rem;
  font-weight: 500;
  line-height: 1.4;
  border: 1px solid rgba(37, 99, 235, 0.15);
  white-space: nowrap;
  transition: background var(--transition), color var(--transition),
    border-color var(--transition);
}

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

/* ===== HERO ACTIONS ===== */
.hero-actions {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--spacing-sm);
}

/* ===== BUTTONS ===== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.75rem 1.75rem;
  border-radius: var(--border-radius);
  font-weight: 600;
  text-decoration: none;
  transition: all var(--transition);
  cursor: pointer;
  border: 2px solid transparent;
  font-size: 0.9375rem;
  letter-spacing: 0.01em;
  line-height: 1.4;
  width: 100%;
  max-width: 280px;
  text-align: center;
}

.btn:hover {
  text-decoration: none;
}

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

.btn-primary:hover {
  background: var(--color-secondary);
  color: white;
  transform: translateY(-2px);
  box-shadow: 0 4px 14px rgba(37, 99, 235, 0.3);
}

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

.btn-secondary:hover {
  background: var(--color-primary);
  color: white;
  transform: translateY(-2px);
  box-shadow: 0 4px 14px rgba(37, 99, 235, 0.15);
}

/* ===== SECTIONS ===== */
.section {
  padding: var(--spacing-lg) 0;
  text-align: center;
}

.section-alt {
  background: var(--color-bg-alt);
  border-top: 1px solid var(--color-border);
  border-bottom: 1px solid var(--color-border);
}

.section h2 {
  font-size: 1.5rem;
  margin-bottom: var(--spacing-md);
}

.section h3 {
  font-size: 1.25rem;
  margin-top: var(--spacing-md);
  margin-bottom: var(--spacing-sm);
}

/* ===== CARD ===== */
.card {
  background: var(--color-surface);
  border-radius: var(--border-radius-lg);
  padding: var(--spacing-md);
  border: 1px solid var(--color-border);
  box-shadow: var(--shadow-sm);
  text-align: center;
  max-width: 860px;
  margin-left: auto;
  margin-right: auto;
}

.section-alt .card {
  background: var(--color-bg);
}

/* ===== TASK & RESULT LISTS ===== */
.task-list,
.results-list {
  list-style: none;
  margin: var(--spacing-md) 0 0;
  padding: 0;
  text-align: left;
}

.task-list li,
.results-list li {
  padding: var(--spacing-sm) var(--spacing-sm) var(--spacing-sm) 2.5rem;
  margin-bottom: var(--spacing-xs);
  background: var(--color-bg-alt);
  border-left: 3px solid var(--color-primary);
  border-radius: var(--border-radius);
  position: relative;
  line-height: 1.6;
  transition: background var(--transition);
}

.task-list li:hover,
.results-list li:hover {
  background: var(--color-accent);
}

.section-alt .task-list li,
.section-alt .results-list li {
  background: var(--color-bg);
}

.section-alt .task-list li:hover,
.section-alt .results-list li:hover {
  background: var(--color-accent);
}

.task-list li::before,
.results-list li::before {
  content: "\2713";
  position: absolute;
  left: var(--spacing-sm);
  color: var(--color-primary);
  font-weight: bold;
  font-size: 1rem;
}

/* ===== TECH STACK GRID ===== */
.tech-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--spacing-sm);
  margin-top: var(--spacing-md);
}

.tech-card {
  background: var(--color-bg-alt);
  border-radius: var(--border-radius);
  padding: var(--spacing-md);
  border: 1px solid var(--color-border);
  transition: box-shadow var(--transition);
  text-align: left;
}

.tech-card:hover {
  box-shadow: var(--shadow-md);
}

.section-alt .tech-card {
  background: var(--color-bg);
}

.tech-card h3 {
  font-size: 0.8125rem;
  margin: 0 0 var(--spacing-xs);
  color: var(--color-primary);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  font-weight: 700;
}

.tech-card .chips {
  justify-content: flex-start;
}

/* ===== DEMO GALLERY ===== */
.demo-actions {
  text-align: center;
  margin: var(--spacing-lg) 0;
}

.demo-gallery {
  margin-top: var(--spacing-xl);
}

.gallery-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--spacing-md);
  margin-top: var(--spacing-md);
}

.gallery-item {
  background: var(--color-surface);
  border-radius: var(--border-radius-lg);
  overflow: hidden;
  border: 1px solid var(--color-border);
  box-shadow: var(--shadow-sm);
  transition: transform var(--transition), box-shadow var(--transition);
}

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

.gallery-item img {
  width: 100%;
  height: auto;
  display: block;
  background: var(--color-bg-alt);
  aspect-ratio: 16 / 9;
  object-fit: cover;
}

.gallery-caption {
  padding: var(--spacing-sm);
  text-align: center;
  font-weight: 500;
  font-size: 0.875rem;
  margin: 0;
  color: var(--color-text-light);
}

/* ===== CONTACT ===== */
.contact-info {
  max-width: 600px;
  margin: 0 auto;
  text-align: left;
}

.contact-info p {
  margin-bottom: var(--spacing-sm);
  font-size: 1rem;
  line-height: 1.7;
  max-width: none;
}

.contact-info strong {
  display: block;
  margin-bottom: 0.125rem;
  color: var(--color-text);
  font-size: 0.8125rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

/* ===== MAIN & FOOTER ===== */
.main {
  min-height: 60vh;
}

.footer {
  background: linear-gradient(180deg, var(--color-bg-alt) 0%, #e2e8f0 100%);
  border-top: 1px solid var(--color-border);
  padding: var(--spacing-lg) 0;
}

.footer-content {
  text-align: center;
}

.footer-content p {
  margin-bottom: var(--spacing-xs);
  font-size: 0.875rem;
  max-width: none;
}

/* ==========================================================
   RESPONSIVE — min-width breakpoints (mobile-first)
   ========================================================== */

/* ~~~~~ 480px — larger phones ~~~~~ */
@media (min-width: 480px) {
  .container {
    padding: 0 var(--spacing-md);
  }

  .hero-actions {
    flex-direction: row;
    justify-content: center;
  }

  .btn {
    width: auto;
    max-width: none;
  }

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

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

  .card {
    padding: var(--spacing-lg);
  }

  .contact-info strong {
    display: inline-block;
    min-width: 130px;
  }
}

/* ~~~~~ 768px — tablets ~~~~~ */
@media (min-width: 768px) {
  h1 {
    font-size: 2.25rem;
  }
  h2 {
    font-size: 1.75rem;
  }
  h3 {
    font-size: 1.375rem;
  }

  .hero {
    padding: var(--spacing-2xl) 0 var(--spacing-xl);
  }

  .hero-title {
    font-size: 2.25rem;
  }

  .hero-subtitle {
    font-size: 1.25rem;
  }

  .hero-description {
    font-size: 1.0625rem;
  }

  .section {
    padding: var(--spacing-xl) 0;
  }

  .section h2 {
    font-size: 1.75rem;
  }

  .gallery-grid {
    grid-template-columns: repeat(3, 1fr);
    gap: var(--spacing-lg);
  }

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

  .tech-card h3 {
    font-size: 0.875rem;
  }
}

/* ~~~~~ 1024px — desktop ~~~~~ */
@media (min-width: 1024px) {
  h1 {
    font-size: 2.75rem;
  }
  h2 {
    font-size: 2rem;
  }
  h3 {
    font-size: 1.5rem;
  }

  .container {
    padding: 0 var(--spacing-lg);
  }

  .hero {
    padding: var(--spacing-2xl) 0 var(--spacing-xl);
  }

  .hero-title {
    font-size: 2.75rem;
  }

  .hero-subtitle {
    font-size: 1.375rem;
  }

  .hero-description {
    font-size: 1.125rem;
  }

  .section {
    padding: var(--spacing-2xl) 0;
  }

  .section h2 {
    font-size: 2rem;
  }

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

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

  .card {
    padding: var(--spacing-xl);
  }
}