Feat: Modify the background color of the agent canvas #3221 (#9020)

### What problem does this PR solve?

Feat: Modify the background color of the agent canvas #3221
### Type of change


- [x] New Feature (non-breaking change which adds functionality)

web/src/components/page-header.tsx

@@ -2,7 +2,7 @@ import { PropsWithChildren } from 'react';
 
 export function PageHeader({ children }: PropsWithChildren) {
   return (
-    <header className="flex justify-between items-center border-b bg-background-header-bar p-5">
+    <header className="flex justify-between items-center border-b bg-text-title-invert p-5">
       {children}
     </header>
   );