Fixed BLT support link clickable area. (#1886)

Co-authored-by: yu-kgr <yu-kgr@yu-kgrnoMacBook-Pro.local>

Author: yu-kgr

site/src/components/SiteHeader.js

@@ -40,7 +40,8 @@ export default function SiteHeader() {
             display: 'flex',
             justifyContent: 'center',
             backgroundColor: 'black',
-            width: '100vw'
+            width: '100vw',
+            zIndex: 100
           }}
         >
           <span