Constant DEFAULT_THEME_CSS 

pub const DEFAULT_THEME_CSS: &str = r#":root {
  --paper: #faf9f5;
  --surface: #ffffff;
  --ink: #1f1e1d;
  --muted: #6b6a67;
  --accent: #cc785c;
  --accent-hover: #b8613f;
  --accent-contrast: #ffffff;
  --border: #e8e6df;
  --radius: 10px;
  --shadow: 0 1px 3px rgba(31,30,29,.06), 0 8px 24px rgba(31,30,29,.05);
  --font-sans: ui-sans-serif, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --font-mono: ui-monospace, "SF Mono", "JetBrains Mono", "Fira Code", Menlo, Consolas, monospace;
  --measure: 720px;
  --space: 1rem;
}
@media (prefers-color-scheme: dark) {
  :root {
    --paper: #1f1e1d;
    --surface: #262624;
    --ink: #f5f4ef;
    --muted: #a3a29e;
    --accent: #e0906f;
    --accent-hover: #ecab8f;
    --accent-contrast: #1f1e1d;
    --border: #3a3936;
    --shadow: 0 1px 3px rgba(0,0,0,.3), 0 8px 24px rgba(0,0,0,.25);
  }
}
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0 auto;
  max-width: min(var(--measure), 92vw);
  padding: 2.5rem 1.25rem 4rem;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}
#root { display: block; }
h1, h2, h3, h4, h5, h6 { line-height: 1.2; font-weight: 600; letter-spacing: -0.011em; margin: 1.6em 0 0.5em; }
h1 { font-size: 2rem; margin-top: 0; }
h2 { font-size: 1.5rem; }
h3 { font-size: 1.25rem; }
p { margin: 0 0 1em; }
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }
small, .muted { color: var(--muted); }
ul, ol { padding-left: 1.4em; margin: 0 0 1em; }
li { margin: 0.25em 0; }
hr { border: none; border-top: 1px solid var(--border); margin: 2em 0; }
button {
  font: inherit;
  font-weight: 550;
  color: var(--accent-contrast);
  background: var(--accent);
  border: none;
  border-radius: var(--radius);
  padding: 0.6em 1.15em;
  cursor: pointer;
  transition: background .15s ease, transform .04s ease;
}
button:hover { background: var(--accent-hover); }
button:active { transform: translateY(1px); }
button:disabled { opacity: .5; cursor: default; }
button.secondary { background: transparent; color: var(--ink); border: 1px solid var(--border); }
input, textarea, select {
  font: inherit;
  color: var(--ink);
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 0.55em 0.7em;
}
input:focus-visible, textarea:focus-visible, select:focus-visible, button:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}
.card, section {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  box-shadow: var(--shadow);
}
code { font-family: var(--font-mono); font-size: 0.9em; background: rgba(31,30,29,.06); padding: 0.1em 0.35em; border-radius: 5px; }
pre { font-family: var(--font-mono); background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 1rem; overflow: auto; }
pre code { background: none; padding: 0; }
table { border-collapse: collapse; width: 100%; }
th, td { text-align: left; padding: 0.5em 0.75em; border-bottom: 1px solid var(--border); }
"#;

The default theme — a small, opinionated design system in Claude’s language: a warm cream surface, a clay accent, ink text, generous spacing, rounded controls, and an automatic dark mode via prefers-color-scheme. Every value is a --token on :root, so a user overrides one line to reskin — and the tokens are the ones largo new --web scaffolds into static/theme.css (--paper, --ink, --accent, --muted, --border, --radius, --shadow), so a project’s theme file reskins these styles too. Ships in every generated page so a LOGOS web app looks designed with zero CSS written, unless the site opts out (ShellTheme::None).