:root {
  --bg-main: #0b0f14;
  --bg-secondary: #111827;
  --bg-card: #0f172a;

  --text-primary: #e5e7eb;
  --text-secondary: #9ca3af;

  --accent: #38bdf8;      /* subtle blue */
  --accent-muted: #1e3a8a;

  --border: #1f2937;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background-color: var(--bg-main);
  color: var(--text-primary);
  line-height: 1.6;
}

header {
  background-color: var(--bg-secondary);
  border-bottom: 1px solid var(--border);
}

nav {
  max-width: 1000px;
  margin: auto;
  padding: 16px 24px;
  display: flex;
  justify-content: center;
  gap: 24px;
}

nav a {
  color: var(--text-secondary);
  text-decoration: none;
  font-weight: 500;
}

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

main {
  max-width: 900px;
  margin: auto;
  padding: 48px 24px;
}

section {
  margin-bottom: 48px;
}

<main>
  <section>
    ...
  </section>
</main>

h1, h2, h3 {
  color: var(--text-primary);
  font-weight: 600;
}

h1 {
  font-size: 2.2rem;
}

h2 {
  font-size: 1.6rem;
  margin-bottom: 12px;
}

p, li {
  color: var(--text-secondary);
  max-width: 75ch;
}

.card {
  background-color: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 24px;
  margin-bottom: 24px;
}

a {
  color: var(--accent);
}

a:hover {
  text-decoration: underline;
}

.button {
  display: inline-block;
  padding: 10px 16px;
  border-radius: 6px;
  background-color: var(--accent-muted);
  color: var(--text-primary);
  text-decoration: none;
}

.button:hover {
  background-color: var(--accent);
}

footer {
  background-color: var(--bg-secondary);
  border-top: 1px solid var(--border);
  text-align: center;
  padding: 24px;
  color: var(--text-secondary);
}