cortex-docs · nick-csu · Oct 1, 2026 · Sep 28, 2026 · Sep 28, 2026 · Oct 1, 2026
diff --git a/e2e/docs-ui-static.spec.ts b/e2e/docs-ui-static.spec.ts
@@ -30,6 +30,29 @@ test.describe('Cloudflare Static Assets export', () => {
     await expect(page.locator('.cortex-cookie-settings-button')).toHaveCount(0);
   });
 
+  for (const appearance of ['light', 'dark']) {
+    for (const [color, background, foreground] of [
+      ['#c2410c', 'rgb(194, 65, 12)', 'rgb(255, 255, 255)'],
+      ['#2563eb', 'rgb(37, 99, 235)', 'rgb(255, 255, 255)'],
+      ['#7c3aed', 'rgb(124, 58, 237)', 'rgb(255, 255, 255)'],
+      ['#ffffff', 'rgb(255, 255, 255)', 'rgb(10, 10, 10)'],
+    ]) {
+      test(`adapts the homepage button text to ${color} in ${appearance} mode`, async ({
+        page,
+      }) => {
+        await page.route('**/api/config*', async (route) => {
+          const response = await route.fetch();
+          const config = await response.json();
+          await route.fulfill({ json: { ...config, primaryColor: color } });
+        });
+        await page.goto(`/?appearance=${appearance}`);
+        const button = page.getByRole('link', { name: 'Getting Started', exact: true });
+        await expect(button).toHaveCSS('background-color', background);
+        await expect(button).toHaveCSS('color', foreground);
+      });
+    }
+  }
+
   test('supports client navigation between generated documentation pages', async ({ page }) => {
     await page.goto('/docs/quickstart');
     await expect(page).toHaveTitle('Petstore Docs');

diff --git a/packages/docs-ui/__tests__/primary-theme.test.ts b/packages/docs-ui/__tests__/primary-theme.test.ts
@@ -0,0 +1,28 @@
+import { describe, expect, it } from 'vitest';
+import { primaryPalette, primaryThemeCss } from '../lib/primary-theme';
+
+describe('primary button contrast', () => {
+  it.each(['#c2410c', '#2563eb', '#7c3aed', '#000000', '#0000ff'])(
+    'uses white text on %s',
+    (color) => {
+      expect(primaryPalette(color).foreground).toBe('#ffffff');
+    },
+  );
+
+  it.each(['#ffffff', '#ffff00', '#00ff00', '#f97316', '#ff0000'])(
+    'uses dark text on a light fill (%s)',
+    (color) => {
+      expect(primaryPalette(color).foreground).toBe('#0a0a0a');
+    },
+  );
+
+  it('keeps the chosen button fill instead of brightening it in dark mode', () => {
+    expect(primaryPalette('#2563eb').background).toBe('rgb(37,99,235)');
+    expect(primaryThemeCss('#2563eb').match(/--color-primary:rgb\(37,99,235\)/g)).toHaveLength(3);
+  });
+
+  it('ignores invalid colors before producing CSS', () => {
+    expect(primaryThemeCss('red')).toBe('');
+    expect(primaryThemeCss('#fff; color:red')).toBe('');
+  });
+});
diff --git a/packages/docs-ui/app/layout.tsx b/packages/docs-ui/app/layout.tsx
@@ -13,6 +13,7 @@ import {
 import { SearchProvider } from '@/components/docs/search-provider';
 import { GoogleAnalytics } from '@/components/docs/google-analytics';
 import { sanitizeSvg } from '@/lib/sanitize-svg';
+import { primaryThemeCss } from '@/lib/primary-theme';
 
 interface LoadedSiteConfig extends SiteConfig {
   customHeadHtml?: string;
@@ -27,33 +28,6 @@ function emptySiteConfig(): LoadedSiteConfig {
   };
 }
 
-function adj(r: number, g: number, b: number, mul: number) {
-  return `rgb(${Math.min(255, Math.round(r * mul))},${Math.min(255, Math.round(g * mul))},${Math.min(255, Math.round(b * mul))})`;
-}
-
-function parsePrimary(hex: string) {
-  const r = parseInt(hex.slice(1, 3), 16);
-  const g = parseInt(hex.slice(3, 5), 16);
-  const b = parseInt(hex.slice(5, 7), 16);
-  const lum = (0.299 * r + 0.587 * g + 0.114 * b) / 255;
-  const lightBgMul = lum < 0.15 ? 1.8 : lum < 0.3 ? 1.3 : 1;
-  const darkBgMul = lum < 0.15 ? 4 : lum < 0.3 ? 2.2 : lum < 0.4 ? 1.4 : 1;
-  const textMul =
-    lum > 0.9 ? 0.45 : lum > 0.7 ? 0.88 : lum > 0.5 ? 0.92 : lum < 0.15 ? 3.5 : lum < 0.3 ? 2 : 1;
-  const lightColor = adj(r, g, b, lightBgMul);
-  const darkColor = adj(r, g, b, darkBgMul);
-  const lightText = adj(r, g, b, textMul);
-  const darkText = adj(r, g, b, darkBgMul);
-  const lightLum = lum * lightBgMul;
-  const darkLum = Math.min(1, lum * darkBgMul);
-  const lightFg = lightLum > 0.5 ? '#0a0a0a' : '#fafafa';
-  const darkFg = darkLum > 0.5 ? '#0a0a0a' : '#fafafa';
-  const targetTintLum = 0.45;
-  const tintMul = lum > 0 ? Math.max(1, targetTintLum / lum) : 6;
-  const cardTint = adj(r, g, b, Math.min(tintMul, 10));
-  return { lightColor, darkColor, lightFg, darkFg, lightText, darkText, cardTint };
-}
-
 function createThemeInitializationScript(defaultTheme: 'light' | 'dark' | 'system'): string {
   return `(()=>{try{const e=document.documentElement,p=new URLSearchParams(location.search).get("appearance");let t=p==="light"||p==="dark"?p:"";if(!t){try{const s=localStorage.getItem("theme");if(s==="light"||s==="dark"||s==="system")t=s}catch{}}if(!t)t="${defaultTheme}";const r=t==="system"?(matchMedia("(prefers-color-scheme: dark)").matches?"dark":"light"):t;e.classList.remove("light","dark");e.classList.add(r);e.style.colorScheme=r}catch{}})();`;
 }
@@ -196,13 +170,7 @@ export default function RootLayout({ children }: { children: React.ReactNode })
   const { customHeadHtml, ...siteConfig } = readSiteConfig();
   const defaultTheme = siteConfig.theme ?? 'system';
 
-  const pc = siteConfig.primaryColor;
-  const primaryCss = pc
-    ? (() => {
-        const p = parsePrimary(pc);
-        return `html{--color-primary:${p.lightColor}!important;--color-primary-foreground:${p.lightFg}!important;--primary-text:${p.lightText};--primary-card-tint:${p.cardTint}}html.dark{--color-primary:${p.darkColor}!important;--color-primary-foreground:${p.darkFg}!important;--primary-text:${p.darkText};--primary-card-tint:${p.cardTint}}@media(prefers-color-scheme:dark){html:not(.light){--color-primary:${p.darkColor}!important;--color-primary-foreground:${p.darkFg}!important;--primary-text:${p.darkText};--primary-card-tint:${p.cardTint}}}`;
-      })()
-    : '';
+  const primaryCss = primaryThemeCss(siteConfig.primaryColor ?? '');
 
   return (
     <html

diff --git a/packages/docs-ui/app/page.tsx b/packages/docs-ui/app/page.tsx
@@ -9,6 +9,7 @@ import {
   type HomeConfig,
 } from '@/components/docs/site-config-provider';
 import { useProjectWatch } from '@/lib/use-project-watch';
+import { primaryThemeCss } from '@/lib/primary-theme';
 
 const COLS = 45;
 const ROWS = 16;
@@ -111,44 +112,13 @@ export default function Home() {
         if (!data) return;
         if (data.home) setHome(data.home);
         if (data.primaryColor && /^#[0-9a-fA-F]{6}$/.test(data.primaryColor)) {
-          const pc = data.primaryColor;
-          const r = parseInt(pc.slice(1, 3), 16);
-          const g = parseInt(pc.slice(3, 5), 16);
-          const b = parseInt(pc.slice(5, 7), 16);
-          const lum = (0.299 * r + 0.587 * g + 0.114 * b) / 255;
-          const a = (m: number) =>
-            `rgb(${Math.min(255, Math.round(r * m))},${Math.min(255, Math.round(g * m))},${Math.min(255, Math.round(b * m))})`;
-          const lbm = lum < 0.15 ? 1.8 : lum < 0.3 ? 1.3 : 1;
-          const dbm = lum < 0.15 ? 4 : lum < 0.3 ? 2.2 : lum < 0.4 ? 1.4 : 1;
-          const tm =
-            lum > 0.9
-              ? 0.45
-              : lum > 0.7
-                ? 0.88
-                : lum > 0.5
-                  ? 0.92
-                  : lum < 0.15
-                    ? 3.5
-                    : lum < 0.3
-                      ? 2
-                      : 1;
-          const tintMul = lum > 0 ? Math.max(1, 0.45 / lum) : 6;
-          const lightColor = a(lbm),
-            darkColor = a(dbm),
-            lightText = a(tm),
-            darkText = a(dbm),
-            cardTint = a(Math.min(tintMul, 10));
-          const lightLum = lum * lbm,
-            darkLum = Math.min(1, lum * dbm);
-          const lightFg = lightLum > 0.5 ? '#0a0a0a' : '#fafafa';
-          const darkFg = darkLum > 0.5 ? '#0a0a0a' : '#fafafa';
           let s = document.querySelector('style[data-primary]') as HTMLStyleElement;
           if (!s) {
             s = document.createElement('style');
             s.setAttribute('data-primary', '');
             document.body.prepend(s);
           }
-          s.textContent = `html{--color-primary:${lightColor}!important;--color-primary-foreground:${lightFg}!important;--primary-text:${lightText};--primary-card-tint:${cardTint}}html.dark{--color-primary:${darkColor}!important;--color-primary-foreground:${darkFg}!important;--primary-text:${darkText};--primary-card-tint:${cardTint}}@media(prefers-color-scheme:dark){html:not(.light){--color-primary:${darkColor}!important;--color-primary-foreground:${darkFg}!important;--primary-text:${darkText};--primary-card-tint:${cardTint}}}`;
+          s.textContent = primaryThemeCss(data.primaryColor);
         }
       })
       .catch(() => {});

diff --git a/packages/docs-ui/components/docs/docs-header.tsx b/packages/docs-ui/components/docs/docs-header.tsx
@@ -379,7 +379,7 @@ export function DocsHeader() {
               )}
               {!hasCustomLogo && (
                 <span className="truncate text-lg font-semibold tracking-tight">
-                  {project || siteTitle || 'Cortex'}
+                  {siteTitle || project || 'Cortex'}
                 </span>
               )}
             </Link>

diff --git a/packages/docs-ui/lib/primary-theme.ts b/packages/docs-ui/lib/primary-theme.ts
@@ -0,0 +1,54 @@
+type Rgb = [number, number, number];
+
+function luminance(color: Rgb): number {
+  const linear = color.map((channel) => {
+    const value = channel / 255;
+    return value <= 0.04045 ? value / 12.92 : ((value + 0.055) / 1.055) ** 2.4;
+  });
+  return 0.2126 * linear[0] + 0.7152 * linear[1] + 0.0722 * linear[2];
+}
+
+export function primaryPalette(hex: string) {
+  const color: Rgb = [
+    parseInt(hex.slice(1, 3), 16),
+    parseInt(hex.slice(3, 5), 16),
+    parseInt(hex.slice(5, 7), 16),
+  ];
+  const brightness = (0.299 * color[0] + 0.587 * color[1] + 0.114 * color[2]) / 255;
+  const adjusted = (multiplier: number) =>
+    `rgb(${color.map((channel) => Math.min(255, Math.round(channel * multiplier))).join(',')})`;
+  const backgroundLuminance = luminance(color);
+  const whiteContrast = 1.05 / (backgroundLuminance + 0.05);
+  const darkContrast = (backgroundLuminance + 0.05) / (luminance([10, 10, 10]) + 0.05);
+  const foreground = whiteContrast >= darkContrast ? '#ffffff' : '#0a0a0a';
+  const textMultiplier =
+    brightness > 0.9
+      ? 0.45
+      : brightness > 0.7
+        ? 0.88
+        : brightness > 0.5
+          ? 0.92
+          : brightness < 0.15
+            ? 3.5
+            : brightness < 0.3
+              ? 2
+              : 1;
+  const darkTextMultiplier =
+    brightness < 0.15 ? 4 : brightness < 0.3 ? 2.2 : brightness < 0.4 ? 1.4 : 1;
+  const tintMultiplier = brightness > 0 ? Math.max(1, 0.45 / brightness) : 6;
+  return {
+    // Keep the configured fill in both themes. Brighten standalone accents separately.
+    background: adjusted(1),
+    foreground,
+    lightText: adjusted(textMultiplier),
+    darkText: adjusted(darkTextMultiplier),
+    cardTint: adjusted(Math.min(tintMultiplier, 10)),
+  };
+}
+
+export function primaryThemeCss(hex: string): string {
+  if (!/^#[0-9a-fA-F]{6}$/.test(hex)) return '';
+  const p = primaryPalette(hex);
+  const shared = `--color-primary:${p.background}!important;--color-primary-foreground:${p.foreground}!important;--primary-card-tint:${p.cardTint}`;
+  return `html{${shared};--primary-text:${p.lightText}}html.dark{${shared};--primary-text:${p.darkText}}@media(prefers-color-scheme:dark){html:not(.light){${shared};--primary-text:${p.darkText}}}`;
+}