/* ===== Reset & Variables ===== */
*, *::before, *::after {
  box-sizing: border-box;
}

:root {
  font-size: 16px;
  --color-bg: #1b2838;
  --color-bg-alt: #171a21;
  --color-surface: #2a475e;
  --color-surface-light: #345670;
  --color-accent: #7fc9f7;
  --color-accent-hover: #a3dbfa;
  --color-text: #c7d5e0;
  --color-text-muted: #adb8c4;
  --color-text-bright: #ffffff;
  --color-success: #4caf50;
  --color-border: rgba(102, 192, 244, 0.15);
  --font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'SF Mono', 'Fira Code', 'Cascadia Code', monospace;
  --radius: 10px;
  --radius-sm: 6px;
  --shadow: 0 4px 16px rgba(0, 0, 0, 0.3);
  --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.2);
  scroll-behavior: smooth;
  scroll-padding-top: 4rem;
}

body {
  margin: 0;
  font-family: var(--font-family);
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
  min-height: 100vh;
}

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

a {
  color: var(--color-accent);
  text-decoration: underline;
  text-decoration-color: rgba(127, 201, 247, 0.5);
  text-underline-offset: 0.15em;
}

a:hover {
  color: var(--color-accent-hover);
  text-decoration-color: currentColor;
}

h1, h2, h3 {
  color: var(--color-text-bright);
  margin-top: 0;
  line-height: 1.3;
}

code {
  font-family: var(--font-mono);
  background: var(--color-bg-alt);
  padding: 0.15em 0.4em;
  border-radius: var(--radius-sm);
  font-size: 0.875em;
  color: var(--color-accent);
}

pre {
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  padding: 0.75rem 1rem;
  overflow-x: auto;
  margin: 0.75rem 0;
}

pre code {
  background: none;
  padding: 0;
  font-size: 0.8125rem;
}

/* ===== Navigation ===== */
.site-nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--color-bg-alt);
  border-bottom: 1px solid var(--color-border);
  /* Avoid backdrop-filter: heavy compositing work; solid bg performs better for TBT/INP */
}

.nav-inner {
  max-width: 1100px;
  margin: 0 auto;
  padding: 0.75rem 1rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.nav-brand {
  font-weight: 700;
  font-size: 1.125rem;
  color: var(--color-text-bright);
  text-decoration: none;
}

.nav-brand:hover {
  color: var(--color-accent);
  text-decoration: none;
}

.nav-links {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  gap: 0.25rem;
  flex-wrap: wrap;
}

.nav-links a {
  display: inline-block;
  padding: 0.35rem 0.7rem;
  border-radius: var(--radius-sm);
  font-size: 0.875rem;
  color: var(--color-text-muted);
  text-decoration: underline;
  text-decoration-color: rgba(173, 184, 196, 0.6);
  text-underline-offset: 0.15em;
  transition: background 0.15s, color 0.15s;
}

.nav-links a:hover {
  background: var(--color-surface);
  color: var(--color-text-bright);
  text-decoration-color: currentColor;
}

.nav-github {
  color: var(--color-accent) !important;
  text-decoration-color: rgba(127, 201, 247, 0.7) !important;
}

.nav-github:hover {
  text-decoration-color: currentColor !important;
}

.nav-github-short {
  display: none;
}

@media (max-width: 399px) {
  .nav-github-long {
    display: none;
  }
  .nav-github-short {
    display: inline;
  }
}

@media (max-width: 400px) {
  .nav-inner {
    padding: 0.5rem 0.75rem;
    gap: 0.25rem;
  }
  .nav-links {
    gap: 0.125rem;
  }
  .nav-links a {
    padding: 0.3rem 0.5rem;
    font-size: 0.8125rem;
  }
  .nav-brand {
    font-size: 1rem;
  }
}

/* ===== Layout ===== */
header, main, footer {
  max-width: 100%;
  margin: 0 auto;
  padding: 0 1rem;
}

section {
  margin-bottom: 3rem;
}

/* Defer layout/paint for below-the-fold sections to reduce main-thread work (TBT/INP) */
section.features,
section.install,
section.usage,
section.troubleshooting {
  content-visibility: auto;
  contain-intrinsic-block-size: 400px;
}

/* ===== Hero ===== */
.hero {
  text-align: center;
  padding: 2rem 0;
}

.hero-image {
  width: 100%;
  max-width: 800px;
  height: auto;
  border-radius: var(--radius);
  margin: 0 auto 1.5rem;
  box-shadow: var(--shadow);
}

.hero h1 {
  font-size: 2rem;
  margin-bottom: 0.5rem;
  letter-spacing: -0.02em;
}

.hero-purpose {
  font-size: 1.125rem;
  color: var(--color-text);
  margin: 0 0 0.5rem;
  max-width: 600px;
  margin-left: auto;
  margin-right: auto;
}

.hero-platform {
  font-size: 0.875rem;
  color: var(--color-accent);
  margin: 0 0 1.5rem;
}

.hero-actions {
  display: flex;
  gap: 0.75rem;
  justify-content: center;
  flex-wrap: wrap;
}

/* ===== Buttons ===== */
.btn {
  display: inline-block;
  padding: 0.65rem 1.5rem;
  border-radius: var(--radius);
  font-size: 0.9375rem;
  font-weight: 600;
  text-decoration: none;
  transition: background 0.15s, transform 0.1s;
}

.btn:hover {
  text-decoration: none;
  transform: translateY(-1px);
}

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

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

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

.btn-secondary:hover {
  background: var(--color-surface-light);
  color: var(--color-text-bright);
}

/* ===== Features ===== */
.features h2 {
  font-size: 1.5rem;
  color: var(--color-accent);
  margin-bottom: 1.25rem;
}

.feature-list {
  list-style: none;
  padding: 0;
  margin: 0;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.feature-card {
  background: var(--color-surface);
  padding: 1.25rem;
  border-radius: var(--radius);
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border);
  display: flex;
  gap: 1rem;
  align-items: flex-start;
  contain: layout style;
}

.feature-card picture {
  flex-shrink: 0;
  width: 64px;
  height: 64px;
  display: block;
}

.feature-icon {
  width: 64px;
  height: 64px;
  flex-shrink: 0;
  border-radius: var(--radius-sm);
  object-fit: cover;
  display: block;
}

.feature-text h3 {
  font-size: 1rem;
  margin: 0 0 0.25rem;
  color: var(--color-accent);
}

.feature-text p {
  margin: 0;
  font-size: 0.9375rem;
  color: var(--color-text-muted);
}

/* ===== Install ===== */
.install h2 {
  font-size: 1.5rem;
  color: var(--color-accent);
  margin-bottom: 1.25rem;
}

.install-prereq {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1rem 1.25rem;
  margin-bottom: 1.5rem;
}

.install-prereq h3 {
  font-size: 1rem;
  margin: 0 0 0.5rem;
  color: var(--color-text-bright);
}

.install-prereq ul {
  margin: 0;
  padding-left: 1.25rem;
}

.install-prereq li {
  margin-bottom: 0.25rem;
  color: var(--color-text-muted);
}

.install-methods {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  margin-bottom: 1.5rem;
}

.install-method {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.25rem;
  contain: layout style;
}

.install-method--primary {
  border-color: var(--color-accent);
  position: relative;
}

.install-method--primary::before {
  content: "Recommended";
  position: absolute;
  top: -0.65rem;
  left: 1rem;
  background: var(--color-accent);
  color: var(--color-bg-alt);
  font-size: 0.75rem;
  font-weight: 700;
  padding: 0.1rem 0.5rem;
  border-radius: 3px;
}

.install-method h3 {
  font-size: 1rem;
  margin: 0 0 0.75rem;
  color: var(--color-text-bright);
}

.install-method ol {
  margin: 0;
  padding-left: 1.25rem;
}

.install-method li {
  margin-bottom: 0.35rem;
  color: var(--color-text-muted);
}

.tun-setup {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.25rem;
}

.tun-setup summary {
  cursor: pointer;
  list-style: none;
}

.tun-setup summary::-webkit-details-marker {
  display: none;
}

.tun-setup summary h3 {
  display: inline;
  font-size: 1rem;
  color: var(--color-accent);
}

.tun-setup summary::before {
  content: "▸ ";
  color: var(--color-accent);
}

.tun-setup[open] summary::before {
  content: "▾ ";
}

.tun-setup ol {
  padding-left: 1.25rem;
}

.tun-setup li {
  margin-bottom: 0.75rem;
  color: var(--color-text-muted);
}

/* ===== Usage ===== */
.usage h2 {
  font-size: 1.5rem;
  color: var(--color-accent);
  margin-bottom: 1.25rem;
}

.usage-steps {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.usage-step {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.25rem;
  display: flex;
  gap: 1rem;
  align-items: flex-start;
  contain: layout style;
}

.step-number {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  min-width: 40px;
  border-radius: 50%;
  background: var(--color-accent);
  color: var(--color-bg-alt);
  font-weight: 700;
  font-size: 1.125rem;
}

.usage-step h3 {
  font-size: 1rem;
  margin: 0 0 0.25rem;
  color: var(--color-text-bright);
}

.usage-step p {
  margin: 0 0 0.25rem;
  color: var(--color-text-muted);
  font-size: 0.9375rem;
}

.text-muted {
  color: var(--color-text-muted);
  font-size: 0.8125rem !important;
}

/* ===== Troubleshooting ===== */
.troubleshooting h2 {
  font-size: 1.5rem;
  color: var(--color-accent);
  margin-bottom: 1.25rem;
}

.faq-list {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.faq-item {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  overflow: hidden;
  contain: layout style;
}

.faq-item summary {
  padding: 1rem 1.25rem;
  cursor: pointer;
  font-weight: 600;
  color: var(--color-text-bright);
  list-style: none;
}

.faq-item summary::-webkit-details-marker {
  display: none;
}

.faq-item summary::before {
  content: "▸ ";
  color: var(--color-accent);
}

.faq-item[open] summary::before {
  content: "▾ ";
}

.faq-item[open] summary {
  border-bottom: 1px solid var(--color-border);
}

.faq-item ul {
  padding: 0.75rem 1.25rem 0.75rem 2.5rem;
  margin: 0;
}

.faq-item li {
  margin-bottom: 0.35rem;
  color: var(--color-text-muted);
}

/* ===== Footer ===== */
footer {
  border-top: 1px solid var(--color-border);
  margin-top: 2rem;
  padding: 2rem 1rem;
}

.footer-inner {
  max-width: 1100px;
  margin: 0 auto;
  text-align: center;
}

.footer-links {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 0.5rem 1.25rem;
  margin-bottom: 1rem;
}

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

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

.footer-copy {
  font-size: 0.8125rem;
  color: var(--color-text-muted);
  margin: 0;
}

/* ===== Tablet: 768px ===== */
@media (min-width: 768px) {
  :root {
    font-size: 17px;
  }

  header, main {
    max-width: 90%;
    margin: 0 auto;
  }

  .hero h1 {
    font-size: 2.5rem;
  }

  .feature-list {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 1rem;
  }

  .install-methods {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 1rem;
  }

  .install-method--primary {
    grid-column: 1 / -1;
  }

  .usage-steps {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 1rem;
  }

  .usage-step {
    flex-direction: column;
    text-align: center;
    align-items: center;
  }
}

/* ===== Desktop: 1280px ===== */
@media (min-width: 1280px) {
  :root {
    font-size: 18px;
  }

  header, main {
    max-width: 1100px;
  }

  .hero {
    padding: 2.5rem 0;
  }

  .hero h1 {
    font-size: 2.75rem;
  }

  .feature-list {
    grid-template-columns: repeat(2, 1fr);
    gap: 1.25rem;
  }
}