fix(preview): align background color and padding with new dashboard theme

vibn-frontend/app/[workspace]/project/[projectId]/(home)/preview/page.tsx

@@ -261,6 +261,7 @@ export default function PreviewTab() {
           display: "flex",
           justifyContent: "center",
           alignItems: "center",
+          padding: "20px 32px",
         }}
       >
         <div
@@ -576,8 +577,9 @@ const canvas: React.CSSProperties = {
   flexDirection: "column",
   alignSelf: "stretch",
   boxSizing: "border-box",
-  padding: "14px 16px 18px",
-  background: "linear-gradient(165deg, #faf8f5 0%, #f4f0ea 42%, #ebe7df 100%)",
+  padding: "16px",
+  background:
+    "radial-gradient(120% 80% at 50% 0%, #ffffff 0%, #f9fafb 52%, #f3f4f6 100%)",
 };
 
 const desktopFrame: React.CSSProperties = {