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

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

body {
  font-family: 'Open Sans', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  font-weight: 400;
  line-height: 1.6;
  color: #333;
  background: #fff;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

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

a {
  color: inherit;
  text-decoration: none;
}

ul, ol {
  list-style: none;
}

button {
  cursor: pointer;
  font-family: inherit;
  border: none;
  background: none;
}

input, textarea, select {
  font-family: inherit;
  font-size: inherit;
}

table {
  border-collapse: collapse;
  width: 100%;
}

iframe {
  border: none;
}

/* === CSS Custom Properties === */
:root {
  /* Colors */
  --color-primary: #1DB954;
  --color-primary-dark: #17a348;
  --color-primary-light: #1ed760;
  --color-primary-accessible: #0f7e34;
  --color-dark-bg: #1a1a2e;
  --color-darker-bg: #0f0f1a;
  --color-dark-card: #16213e;
  --color-dark-card-alt: #1a1a3e;
  --color-light-bg: #f5f5f7;
  --color-white: #ffffff;
  --color-text: #333333;
  --color-text-light: #666666;
  --color-text-muted: #999999;
  --color-text-white: #ffffff;
  --color-text-white-muted: rgba(255, 255, 255, 0.7);
  --color-border: #e0e0e0;
  --color-border-dark: rgba(255, 255, 255, 0.1);

  /* Typography — Fluid Scaling */
  --font-family: 'Open Sans', sans-serif;
  --font-size-xs: 0.75rem;
  --font-size-sm: 0.875rem;
  --font-size-base: 1rem;
  --font-size-lg: 1.125rem;
  --font-size-xl: 1.25rem;
  --font-size-2xl: 1.5rem;
  --font-size-3xl: clamp(1.75rem, 3vw, 2.25rem);
  --font-size-4xl: clamp(2rem, 4vw, 2.75rem);
  --font-size-5xl: clamp(2.5rem, 5vw, 3.5rem);

  /* Spacing */
  --spacing-xs: 0.5rem;
  --spacing-sm: 1rem;
  --spacing-md: 1.5rem;
  --spacing-lg: 2rem;
  --spacing-xl: 3rem;
  --spacing-2xl: 4rem;
  --spacing-3xl: 7rem;

  /* Layout */
  --container-max: 1200px;
  --container-padding: 1.5rem;

  /* Borders */
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --radius-xl: 16px;
  --radius-full: 50%;
  --radius-pill: 100px;

  /* Shadows — Refined Depth */
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.08);
  --shadow-lg: 0 8px 30px rgba(0, 0, 0, 0.12);
  --shadow-xl: 0 12px 32px rgba(0, 0, 0, 0.12);

  /* Easing & Transitions */
  --ease-out: cubic-bezier(0.16, 1, 0.3, 1);
  --transition-fast: 0.15s var(--ease-out);
  --transition-base: 0.3s var(--ease-out);
  --transition-slow: 0.5s var(--ease-out);
}

/* === Selection Color === */
::selection {
  background: var(--color-primary);
  color: #fff;
}

/* === Typography === */
h1, h2, h3, h4, h5, h6 {
  font-weight: 700;
  line-height: 1.2;
  color: inherit;
}

h1, h2, h3 {
  letter-spacing: -0.02em;
}

h1 { font-size: var(--font-size-5xl); }
h2 { font-size: var(--font-size-4xl); }
h3 { font-size: var(--font-size-3xl); }
h4 { font-size: var(--font-size-2xl); }
h5 { font-size: var(--font-size-xl); }
h6 { font-size: var(--font-size-lg); }

p {
  margin-bottom: 1rem;
  line-height: 1.7;
}

p:last-child {
  margin-bottom: 0;
}

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

.section {
  padding: var(--spacing-3xl) 0;
}

.section--dark {
  background: var(--color-dark-bg);
  color: var(--color-text-white);
}

.section--darker {
  background: var(--color-darker-bg);
  color: var(--color-text-white);
}

.section--light {
  background: var(--color-light-bg);
  color: var(--color-text);
}

.section__header {
  text-align: center;
  margin-bottom: var(--spacing-2xl);
}

.section__title {
  font-size: var(--font-size-4xl);
  font-weight: 700;
  margin-bottom: var(--spacing-sm);
}

.section__subtitle {
  font-size: var(--font-size-lg);
  color: var(--color-text-light);
  max-width: 700px;
  margin: 0 auto;
}

.section--dark .section__subtitle,
.section--darker .section__subtitle {
  color: var(--color-text-white-muted);
}

/* === Grid System === */
.grid {
  display: grid;
  gap: var(--spacing-lg);
}

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

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

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

/* === Cards === */
.card {
  background: var(--color-white);
  border-radius: var(--radius-lg);
  padding: var(--spacing-lg);
  box-shadow: var(--shadow-sm);
  transition: transform var(--transition-base), box-shadow var(--transition-base);
}

.card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-lg);
}

.card--dark {
  background: var(--color-dark-card);
  color: var(--color-text-white);
  border: 1px solid var(--color-border-dark);
  transition: transform var(--transition-base), box-shadow var(--transition-base), border-color var(--transition-base);
}

.card--dark:hover {
  border-color: var(--color-primary);
  box-shadow: 0 0 20px rgba(29, 185, 84, 0.15);
}

.card--glass {
  background: rgba(255, 255, 255, 0.05);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border: 1px solid rgba(255, 255, 255, 0.08);
  color: var(--color-text-white);
}

.card__icon {
  width: 48px;
  height: 48px;
  margin-bottom: var(--spacing-sm);
}

.card__title {
  font-size: var(--font-size-xl);
  font-weight: 700;
  margin-bottom: var(--spacing-xs);
}

.card__text {
  font-size: var(--font-size-base);
  color: var(--color-text-light);
  line-height: 1.6;
}

.card--dark .card__text,
.card--glass .card__text {
  color: var(--color-text-white-muted);
}

/* === Buttons === */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.8rem 2rem;
  border-radius: var(--radius-pill);
  font-weight: 600;
  font-size: var(--font-size-base);
  transition: all var(--transition-base);
  text-decoration: none;
  gap: 0.5rem;
  white-space: nowrap;
}

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

.btn--primary:hover {
  background: var(--color-primary-light);
  transform: translateY(-1px);
  box-shadow: 0 0 20px rgba(29, 185, 84, 0.3);
}

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

.btn--outline:hover {
  background: var(--color-primary);
  color: var(--color-white);
  transform: translateY(-1px);
  box-shadow: 0 0 20px rgba(29, 185, 84, 0.3);
}

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

.btn--white:hover {
  background: var(--color-light-bg);
  transform: translateY(-1px);
  box-shadow: 0 0 20px rgba(255, 255, 255, 0.2);
}

.btn--glass {
  background: rgba(255, 255, 255, 0.1);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border: 1px solid rgba(255, 255, 255, 0.2);
  color: var(--color-text-white);
}

.btn--glass:hover {
  background: rgba(255, 255, 255, 0.18);
  transform: translateY(-1px);
  box-shadow: 0 0 20px rgba(255, 255, 255, 0.1);
}

.btn--arrow::after {
  content: '\2192';
  margin-left: 0.25rem;
  transition: transform var(--transition-fast);
}

.btn--arrow:hover::after {
  transform: translateX(3px);
}

.btn:active {
  transform: scale(0.97);
}

.btn:disabled,
.btn[disabled] {
  opacity: 0.5;
  cursor: not-allowed;
  pointer-events: none;
}

.btn--sm {
  padding: 0.5rem 1.25rem;
  font-size: var(--font-size-sm);
}

.btn--lg {
  padding: 1rem 2.5rem;
  font-size: var(--font-size-lg);
}

/* === Two-Column Layout === */
.split {
  display: flex;
  align-items: center;
  gap: var(--spacing-2xl);
}

.split--reverse {
  flex-direction: row-reverse;
}

.split__content {
  flex: 1;
}

.split__media {
  flex: 1;
}

.split__media img {
  border-radius: var(--radius-lg);
  width: 100%;
  aspect-ratio: 16 / 9;
  object-fit: cover;
}

/* === Glassmorphism Utility === */
.glass {
  background: rgba(255, 255, 255, 0.05);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border: 1px solid rgba(255, 255, 255, 0.08);
}

/* === Gradient Text Utility === */
.gradient-text {
  background: linear-gradient(135deg, #1DB954, #00d9ff);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}

/* === Scroll-Triggered Fade-In === */
.fade-up {
  opacity: 0;
  transform: translateY(16px);
  transition: opacity 0.6s var(--ease-out), transform 0.6s var(--ease-out);
}

.fade-up.visible {
  opacity: 1;
  transform: translateY(0);
}

/* === Text Utilities === */
.text-center { text-align: center; }
.text-left { text-align: left; }
.text-right { text-align: right; }
.text-primary { color: var(--color-primary); }
.text-muted { color: var(--color-text-muted); }
.text-white { color: var(--color-text-white); }
.font-light { font-weight: 300; }
.font-semibold { font-weight: 600; }
.font-bold { font-weight: 700; }

/* === Spacing Utilities === */
.mt-1 { margin-top: var(--spacing-sm); }
.mt-2 { margin-top: var(--spacing-lg); }
.mt-3 { margin-top: var(--spacing-xl); }
.mb-1 { margin-bottom: var(--spacing-sm); }
.mb-2 { margin-bottom: var(--spacing-lg); }
.mb-3 { margin-bottom: var(--spacing-xl); }

/* === Disclaimer === */
.disclaimer {
  background: var(--color-light-bg);
  border-left: 4px solid var(--color-primary);
  padding: var(--spacing-lg);
  margin-top: var(--spacing-2xl);
  border-radius: var(--radius-sm);
}

.disclaimer__title {
  font-size: var(--font-size-lg);
  font-weight: 700;
  margin-bottom: var(--spacing-xs);
}

.disclaimer__text {
  font-size: var(--font-size-sm);
  color: var(--color-text-light);
  line-height: 1.7;
}

/* === Skip Link === */
.skip-link {
  position: absolute;
  top: -100%;
  left: 50%;
  transform: translateX(-50%);
  background: var(--color-primary);
  color: #fff;
  padding: 0.75rem 1.5rem;
  border-radius: var(--radius-pill);
  font-weight: 600;
  z-index: 10000;
  transition: top 0.2s;
}

.skip-link:focus {
  top: 1rem;
}

/* === Screen Reader Only === */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* === Responsive === */
@media (max-width: 1024px) and (min-width: 769px) {
  .grid--3 {
    grid-template-columns: repeat(2, 1fr);
  }

  .grid--4 {
    grid-template-columns: repeat(2, 1fr);
  }

  .split {
    gap: var(--spacing-lg);
  }
}

@media (max-width: 768px) {
  .section { padding: var(--spacing-2xl) 0; }

  .grid--2,
  .grid--3,
  .grid--4 {
    grid-template-columns: 1fr;
  }

  .split {
    flex-direction: column;
  }

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

@media (max-width: 480px) {
  :root {
    --container-padding: 1rem;
  }
  .btn--lg {
    padding: 0.75rem 1.75rem;
    font-size: var(--font-size-base);
  }
}

/* === Focus Visible === */
a:focus-visible, button:focus-visible, input:focus-visible, select:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}
.btn:focus-visible {
  box-shadow: 0 0 0 3px rgba(29, 185, 84, 0.3);
}

/* === Reduced Motion === */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
  .fade-up {
    opacity: 1;
    transform: none;
  }
}