fix(frontend): better visualisation of current path on menu (#2122)

# Description

Please include a summary of the changes and the related issue. Please
also include relevant motivation and context.

## Checklist before requesting a review

Please delete options that are not relevant.

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented hard-to-understand areas
- [ ] I have ideally added tests that prove my fix is effective or that
my feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged

## Screenshots (if appropriate):

frontend/lib/components/Menu/components/MenuButton/MenuButton.module.scss

@@ -10,6 +10,12 @@
   padding: Spacings.$spacing03;
   border-radius: 5px;
   overflow: hidden;
+  border-left: 2px solid transparent;
+
+  &.selected {
+    border-left: 2px solid Colors.$primary;
+    border-radius: 0 5px 5px 0;
+  }
 
   .left {
     display: flex;
@@ -35,18 +41,4 @@
   &:hover {
     background-color: Colors.$lightest-black;
   }
-
-  &.selected {
-    border-color: Colors.$accent;
-  }
-
-  &.gold {
-    &:hover {
-      border-color: Colors.$gold;
-    }
-
-    &.selected {
-      border-color: Colors.$gold;
-    }
-  }
 }