/* ==========================================================================
   INTERVAL Landing Site — Shared Stylesheet
   Dark theme, minimalist radio aesthetic, mobile-first responsive
   ========================================================================== */

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

/* ==========================================================================
   Custom Properties
   ========================================================================== */

:root {
  --bg:             #0a0a0a;
  --surface:        #141414;
  --surface-raised: #1f1f1f;
  --border:         #2a2a2a;
  --border-light:   #3a3a3a;

  --text:           #f0f0f0;
  --text-secondary: #c0c0c0;
  --text-muted:     #707070;

  --accent:         #ffffff;
  --accent-dim:     #a0a0a0;

  --signal-green:   #4ade80;
  --signal-red:     #f87171;

  --font-body: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;

  --space-xs:  0.25rem;
  --space-sm:  0.5rem;
  --space-md:  1rem;
  --space-lg:  1.5rem;
  --space-xl:  2rem;
  --space-2xl: 3rem;
  --space-3xl: 4rem;
  --space-4xl: 6rem;
  --space-5xl: 8rem;

  --container-max: 1120px;
  --nav-height: 64px;
  --radius:     8px;
  --radius-lg:  12px;

  --ease-out: cubic-bezier(0.16, 1, 0.3, 1);
  --duration: 0.2s;
  --duration-slow: 0.4s;
}

/* ==========================================================================
   Reset
   ========================================================================== */

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

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

body {
  font-family: var(--font-body);
  font-size: 1rem;
  line-height: 1.6;
  color: var(--text);
  background: var(--bg);
  -webkit-font-smoothing: antialiased;
  overflow-x: hidden;
}

img, svg { display: block; max-width: 100%; }
a { color: inherit; text-decoration: none; }
ul, ol { list-style: none; }
button { cursor: pointer; background: none; border: none; font: inherit; color: inherit; }

/* ==========================================================================
   Typography
   ========================================================================== */

h1, h2, h3, h4, h5, h6 {
  font-weight: 700;
  line-height: 1.15;
  letter-spacing: -0.02em;
  color: var(--text);
}

h1 { font-size: clamp(2.25rem, 5vw + 1rem, 4rem); font-weight: 800; letter-spacing: -0.03em; }
h2 { font-size: clamp(1.75rem, 3vw + 0.5rem, 2.75rem); }
h3 { font-size: clamp(1.125rem, 2vw + 0.25rem, 1.5rem); }

p { color: var(--text-secondary); max-width: 65ch; }

.lead {
  font-size: clamp(1.125rem, 1.5vw + 0.5rem, 1.375rem);
  line-height: 1.7;
  color: var(--text-secondary);
}

.text-center { text-align: center; }
.text-center p { margin-inline: auto; }

.mono { font-family: var(--font-mono); }

.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;
}

/* ==========================================================================
   Layout
   ========================================================================== */

.container {
  width: 100%;
  max-width: var(--container-max);
  margin-inline: auto;
  padding-inline: var(--space-lg);
}

@media (min-width: 640px)  { .container { padding-inline: var(--space-xl); } }
@media (min-width: 1024px) { .container { padding-inline: var(--space-2xl); } }

.section {
  padding-block: var(--space-4xl);
}

.section-alt {
  background: var(--surface);
}

@media (min-width: 768px) {
  .section { padding-block: var(--space-5xl); }
}

/* ==========================================================================
   Navigation
   ========================================================================== */

.nav {
  position: fixed;
  top: 0; left: 0; right: 0;
  z-index: 1000;
  height: var(--nav-height);
  background: rgba(10, 10, 10, 0.88);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}

.nav-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
  max-width: var(--container-max);
  margin-inline: auto;
  padding-inline: var(--space-lg);
}

.nav-logo img {
  height: 28px;
  width: auto;
}

/* Desktop links — hidden on mobile */
.nav-links {
  display: none;
  align-items: center;
  gap: var(--space-xl);
}

.nav-links a {
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--text-secondary);
  transition: color var(--duration) var(--ease-out);
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--text);
}

.nav-links .btn {
  margin-left: var(--space-sm);
}

/* Hamburger */
.nav-hamburger {
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 5px;
  width: 28px;
  height: 28px;
  cursor: pointer;
}

.nav-hamburger span {
  display: block;
  width: 100%;
  height: 2px;
  background: var(--text);
  border-radius: 1px;
  transition: transform var(--duration) var(--ease-out), opacity var(--duration) var(--ease-out);
}

.nav-hamburger.open span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav-hamburger.open span:nth-child(2) { opacity: 0; }
.nav-hamburger.open span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* Mobile menu overlay */
.nav-mobile {
  display: none;
  position: fixed;
  top: var(--nav-height);
  left: 0; right: 0; bottom: 0;
  background: rgba(10, 10, 10, 0.97);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  padding: var(--space-2xl) var(--space-lg);
  z-index: 999;
}

.nav-mobile.open {
  display: flex;
  flex-direction: column;
  gap: var(--space-lg);
}

.nav-mobile a {
  font-size: 1.25rem;
  font-weight: 500;
  color: var(--text-secondary);
  padding-block: var(--space-sm);
  transition: color var(--duration) var(--ease-out);
}

.nav-mobile a:hover { color: var(--text); }

@media (min-width: 768px) {
  .nav-links { display: flex; }
  .nav-hamburger { display: none; }
}

/* ==========================================================================
   Hero
   ========================================================================== */

.hero {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  min-height: calc(100vh - var(--nav-height));
  padding: var(--space-3xl) var(--space-lg);
  padding-top: calc(var(--nav-height) + var(--space-3xl));
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  top: -20%;
  left: 50%;
  transform: translateX(-50%);
  width: 600px;
  height: 600px;
  background: radial-gradient(circle, rgba(255,255,255,0.03) 0%, transparent 70%);
  pointer-events: none;
}

.hero-logo {
  height: 60px;
  width: auto;
  margin-bottom: var(--space-xl);
}

@media (min-width: 640px) {
  .hero-logo { height: 80px; }
}

.hero h1 { margin-bottom: var(--space-lg); }

.hero .lead {
  margin-bottom: var(--space-2xl);
  max-width: 600px;
  margin-inline: auto;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-md);
  justify-content: center;
}

.hero-compact {
  min-height: auto;
  padding-top: calc(var(--nav-height) + var(--space-4xl));
  padding-bottom: var(--space-3xl);
}

/* ==========================================================================
   Buttons
   ========================================================================== */

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
  padding: 0.75rem 1.75rem;
  font-size: 0.9375rem;
  font-weight: 600;
  border-radius: var(--radius);
  transition: all var(--duration) var(--ease-out);
  white-space: nowrap;
  cursor: pointer;
  border: none;
}

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

.btn-primary:hover {
  background: #e0e0e0;
  transform: translateY(-1px);
  box-shadow: 0 4px 16px rgba(255,255,255,0.1);
}

.btn-secondary {
  background: transparent;
  color: var(--text);
  border: 1px solid var(--border-light);
}

.btn-secondary:hover {
  border-color: var(--text-muted);
  background: rgba(255,255,255,0.04);
  transform: translateY(-1px);
}

.btn-sm { padding: 0.5rem 1.25rem; font-size: 0.8125rem; }
.btn-lg { padding: 1rem 2.25rem; font-size: 1rem; }

/* ==========================================================================
   Cards
   ========================================================================== */

.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  transition: transform var(--duration-slow) var(--ease-out),
              border-color var(--duration) var(--ease-out),
              box-shadow var(--duration-slow) var(--ease-out);
}

.card:hover {
  transform: translateY(-4px);
  border-color: var(--border-light);
  box-shadow: 0 8px 32px rgba(0,0,0,0.3);
}

.card h3 { margin-bottom: var(--space-sm); }
.card p { font-size: 0.9375rem; }

.card-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-xl);
}

@media (min-width: 640px) {
  .card-grid { grid-template-columns: repeat(2, 1fr); }
}

/* ==========================================================================
   Steps
   ========================================================================== */

.steps {
  display: grid;
  gap: var(--space-2xl);
}

.step {
  display: flex;
  gap: var(--space-lg);
  align-items: flex-start;
}

.step-number {
  flex-shrink: 0;
  width: 48px;
  height: 48px;
  display: flex;
  align-items: center;
  justify-content: center;
  border: 2px solid var(--border-light);
  border-radius: 50%;
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: 1.125rem;
  color: var(--text);
  background: var(--surface);
}

.step h3 { margin-bottom: var(--space-xs); }
.step p { font-size: 0.9375rem; }

@media (min-width: 768px) {
  .steps-horizontal {
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  }
  .steps-horizontal .step {
    flex-direction: column;
    align-items: center;
    text-align: center;
  }
}

/* ==========================================================================
   Rules / Manifesto
   ========================================================================== */

.rules {
  counter-reset: rule;
  max-width: 600px;
}

.rule {
  counter-increment: rule;
  display: flex;
  gap: var(--space-lg);
  align-items: baseline;
  padding-block: var(--space-md);
  border-bottom: 1px solid var(--border);
  font-size: 1.125rem;
  color: var(--text-secondary);
}

.rule::before {
  content: counter(rule);
  font-family: var(--font-mono);
  font-size: 0.8125rem;
  font-weight: 700;
  color: var(--text-muted);
  min-width: 1.5rem;
}

.rules-closing {
  margin-top: var(--space-xl);
  font-family: var(--font-mono);
  font-size: 0.875rem;
  color: var(--text-muted);
  letter-spacing: 0.02em;
}

/* ==========================================================================
   Principles Strip
   ========================================================================== */

.principles {
  padding-block: var(--space-2xl);
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
  background: var(--surface);
}

.principles-inner {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: var(--space-md) var(--space-lg);
  max-width: var(--container-max);
  margin-inline: auto;
  padding-inline: var(--space-lg);
}

.principle {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  font-weight: 500;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--text-muted);
}

.principle-sep {
  color: var(--border-light);
  user-select: none;
}

/* ==========================================================================
   Philosophy List
   ========================================================================== */

.philosophy-list li {
  padding: var(--space-md) 0;
  border-bottom: 1px solid var(--border);
  color: var(--text-secondary);
  font-size: 1rem;
  line-height: 1.7;
}

.philosophy-list li strong {
  color: var(--text);
}

/* ==========================================================================
   Radio Rules (About page ordered list)
   ========================================================================== */

.radio-rules {
  counter-reset: radio-rule;
  max-width: 600px;
}

.radio-rules li {
  counter-increment: radio-rule;
  display: flex;
  gap: var(--space-lg);
  align-items: baseline;
  padding-block: var(--space-md);
  border-bottom: 1px solid var(--border);
  font-size: 1.125rem;
  color: var(--text-secondary);
}

.radio-rules li::before {
  content: counter(radio-rule);
  font-family: var(--font-mono);
  font-size: 0.8125rem;
  font-weight: 700;
  color: var(--text-muted);
  min-width: 1.5rem;
}

.manifesto-closing {
  margin-top: var(--space-xl);
  font-family: var(--font-mono);
  font-size: 0.875rem;
  color: var(--text-muted);
}

/* ==========================================================================
   Footer
   ========================================================================== */

.footer {
  background: var(--surface);
  border-top: 1px solid var(--border);
  padding-block: var(--space-3xl) var(--space-2xl);
}

.footer-inner {
  display: flex;
  flex-direction: column;
  gap: var(--space-xl);
  max-width: var(--container-max);
  margin-inline: auto;
  padding-inline: var(--space-lg);
}

@media (min-width: 640px) {
  .footer-inner {
    flex-direction: row;
    justify-content: space-between;
    align-items: flex-start;
  }
}

.footer-brand img {
  height: 24px;
  width: auto;
  margin-bottom: var(--space-sm);
}

.footer-brand p {
  font-size: 0.875rem;
  color: var(--text-muted);
}

.footer-links ul {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-md) var(--space-xl);
}

.footer-links a {
  font-size: 0.875rem;
  color: var(--text-secondary);
  transition: color var(--duration) var(--ease-out);
}

.footer-links a:hover { color: var(--text); }

.footer-bottom {
  max-width: var(--container-max);
  margin-inline: auto;
  padding-inline: var(--space-lg);
  padding-top: var(--space-xl);
  margin-top: var(--space-xl);
  border-top: 1px solid var(--border);
}

.footer-bottom p {
  font-size: 0.8125rem;
  color: var(--text-muted);
}

/* ==========================================================================
   Morse Line Decoration
   ========================================================================== */

.morse-line {
  height: 3px;
  background: repeating-linear-gradient(
    90deg,
    var(--text-muted) 0px, var(--text-muted) 6px,
    transparent 6px, transparent 12px,
    var(--text-muted) 12px, var(--text-muted) 32px,
    transparent 32px, transparent 38px,
    var(--text-muted) 38px, var(--text-muted) 44px,
    transparent 44px, transparent 50px
  );
  border-radius: 2px;
  opacity: 0.15;
}

/* ==========================================================================
   Signal Animations
   ========================================================================== */

@keyframes pulse-signal {
  0%, 100% { opacity: 1; transform: scale(1); }
  50% { opacity: 0.4; transform: scale(1.15); }
}

.signal-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: var(--text);
  animation: pulse-signal 2s ease-in-out infinite;
}

/* ==========================================================================
   Scroll Fade-in
   ========================================================================== */

.fade-in {
  opacity: 0;
  transform: translateY(24px);
  transition: opacity 0.6s var(--ease-out), transform 0.6s var(--ease-out);
}

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

/* ==========================================================================
   Feature Cards (Features page)
   ========================================================================== */

.features-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1.5rem;
}

@media (min-width: 640px)  { .features-grid { grid-template-columns: repeat(2, 1fr); } }
@media (min-width: 1024px) { .features-grid { grid-template-columns: repeat(3, 1fr); } }

.feature-card {
  position: relative;
  background: rgba(255,255,255,0.03);
  border: 1px solid rgba(255,255,255,0.06);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  overflow: hidden;
  transition: border-color 0.3s ease, transform 0.3s ease;
}

.feature-card:hover {
  border-color: rgba(255,255,255,0.15);
  transform: translateY(-2px);
}

.feature-card-morse {
  position: absolute;
  bottom: 0; left: var(--space-xl); right: var(--space-xl);
  height: 2px;
  background: repeating-linear-gradient(
    90deg,
    rgba(255,255,255,0.1) 0px, rgba(255,255,255,0.1) 4px,
    transparent 4px, transparent 8px,
    rgba(255,255,255,0.1) 8px, rgba(255,255,255,0.1) 16px,
    transparent 16px, transparent 20px
  );
}

.feature-card-category {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.65rem;
  font-weight: 500;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  padding: 0.25rem 0.6rem;
  border-radius: 4px;
  margin-bottom: 0.75rem;
}

.feature-card-category.comm   { color: #4ade80; background: rgba(74,222,128,0.1); }
.feature-card-category.train  { color: #facc15; background: rgba(250,204,21,0.1); }
.feature-card-category.field  { color: #38bdf8; background: rgba(56,189,248,0.1); }
.feature-card-category.adv    { color: #c084fc; background: rgba(192,132,252,0.1); }

.feature-card h3 {
  font-size: 1.2rem;
  font-weight: 600;
  margin: 0 0 0.5rem;
}

.feature-card p {
  font-size: 0.9rem;
  line-height: 1.6;
  color: rgba(255,255,255,0.6);
  margin: 0;
}

/* ==========================================================================
   Download Page
   ========================================================================== */

.dl-hero {
  text-align: center;
  padding: calc(var(--nav-height) + var(--space-4xl)) 0 var(--space-2xl);
}

.dl-hero-icon {
  width: 160px;
  height: 160px;
  border-radius: 2rem;
  box-shadow: 0 0 60px rgba(255,255,255,0.08), 0 0 120px rgba(100,140,255,0.06);
  margin: 0 auto var(--space-xl);
}

.dl-options {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1.5rem;
  padding-block: var(--space-xl);
}

@media (min-width: 768px) {
  .dl-options { grid-template-columns: repeat(3, 1fr); }
}

.dl-card {
  background: rgba(255,255,255,0.04);
  border: 1px solid rgba(255,255,255,0.08);
  border-radius: 1rem;
  padding: 2.5rem 2rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  transition: border-color 0.2s ease, background 0.2s ease;
}

.dl-card:hover {
  border-color: rgba(255,255,255,0.15);
  background: rgba(255,255,255,0.06);
}

.dl-card-disabled {
  opacity: 0.4;
  pointer-events: none;
}

.dl-card-icon {
  width: 48px; height: 48px;
  margin-bottom: 1.5rem;
  color: rgba(255,255,255,0.7);
}

.dl-card-label {
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: rgba(255,255,255,0.4);
  margin-bottom: 0.5rem;
}

.dl-card h3 {
  font-size: 1.25rem;
  font-weight: 600;
  margin: 0 0 0.75rem;
}

.dl-card p {
  color: rgba(255,255,255,0.6);
  font-size: 0.95rem;
  line-height: 1.6;
  margin: 0 0 0.5rem;
}

.dl-card-detail {
  color: rgba(255,255,255,0.35);
  font-size: 0.85rem;
  margin: 0 0 1.5rem;
}

.dl-card-btn {
  display: inline-block;
  padding: 0.85rem 2rem;
  border-radius: 0.5rem;
  font-weight: 600;
  font-size: 0.95rem;
  transition: background 0.2s ease, transform 0.1s ease;
  margin-top: auto;
}

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

.dl-card-btn.primary { background: #fff; color: #0a0a0a; }
.dl-card-btn.primary:hover { background: #e0e0e0; }

.dl-card-btn.secondary {
  background: rgba(255,255,255,0.1);
  color: #fff;
  border: 1px solid rgba(255,255,255,0.2);
}
.dl-card-btn.secondary:hover { background: rgba(255,255,255,0.15); }

.dl-card-note {
  font-size: 0.78rem;
  color: rgba(255,255,255,0.3);
  margin-top: 1rem;
  line-height: 1.4;
}

.dl-card-coming {
  font-size: 0.85rem;
  color: rgba(255,255,255,0.3);
  font-weight: 500;
  margin-top: auto;
  padding: 0.85rem 2rem;
}

/* Getting Started */
.gs-steps {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1.5rem;
}

@media (min-width: 640px)  { .gs-steps { grid-template-columns: repeat(2, 1fr); } }
@media (min-width: 768px)  { .gs-steps { grid-template-columns: repeat(4, 1fr); } }

.gs-step { text-align: center; }

.gs-step-number {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 40px; height: 40px;
  border-radius: 50%;
  border: 1px solid rgba(255,255,255,0.15);
  font-family: var(--font-mono);
  font-size: 0.9rem;
  font-weight: 600;
  color: rgba(255,255,255,0.6);
  margin-bottom: 1rem;
}

.gs-step h3 { font-size: 1rem; font-weight: 600; margin: 0 0 0.5rem; }
.gs-step p { font-size: 0.9rem; color: rgba(255,255,255,0.5); line-height: 1.5; margin: 0; }

/* System Requirements */
.sys-req-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1.5rem;
  max-width: 800px;
  margin: 0 auto;
}

@media (min-width: 768px) { .sys-req-grid { grid-template-columns: repeat(3, 1fr); } }

.sys-req-item {
  text-align: center;
  padding: 1.5rem;
  background: rgba(255,255,255,0.02);
  border: 1px solid rgba(255,255,255,0.06);
  border-radius: 0.75rem;
}

.sys-req-label {
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: rgba(255,255,255,0.4);
  margin: 0 0 0.5rem;
}

.sys-req-detail {
  font-size: 0.9rem;
  color: rgba(255,255,255,0.6);
  line-height: 1.5;
  margin: 0;
}

/* ==========================================================================
   Print
   ========================================================================== */

@media print {
  .nav, .nav-mobile, .footer { display: none; }
  body { background: #fff; color: #111; }
  .card { border: 1px solid #ccc; box-shadow: none; }
}