Add transparency to text highlight color

In order avoid the problem of hiding parts of the characters
adjacent to the highlighted text, the highlighting background
needs to be partially transparent.

src/app/components/HighlightedText/index.tsx

@@ -26,7 +26,7 @@ export interface HighlightOptions {
 }
 
 const defaultHighlightStyle: SxProps = {
-  background: '#FFFF54',
+  background: '#FFFF5480',
   padding: '4px',
   margin: '-4px',
 }