exclude menu and TOC items from the visited link styles for better UX

for better UX, menu and TOC items style should indicate only one thing, which is the current read item

website/src/css/custom.css

@@ -137,7 +137,7 @@ a.contents__link.contents__link--active {
   font-weight: 600;
 }
 
-a:visited {
+a:visited:not(.menu__link, .table-of-contents__link) {
   color: var(--ifm-color-primary);
 }