[DX] Improve right sidebar ToC hover contrast and accessibility (#960)

- Add padding and border-radius to ToC links for a clearer hover target
- Add background-color and color transitions for smooth visual feedback
- Add focus-visible style for keyboard navigation accessibility

Incorporates PR #960 from @kavyakapoor420 with gemini review suggestions applied:
expanded transition to include color, added focus-visible alongside hover.

Signed-off-by: Lee Calcote <lee.calcote@layer5.io>

Author: leecalcote

assets/scss/_styles_project.scss

@@ -378,8 +378,12 @@ a:not([href]):not([class]):hover {
   #TableOfContents {
     a {
       color: $lightslategray;
+      padding: 0.25rem 0.5rem;
+      border-radius: 4px;
+      transition: background-color 0.2s ease, color 0.2s ease;
 
-      &:hover {
+      &:hover,
+      &:focus-visible {
         color: $white;
         text-decoration: none;
         background-color: rgba($primary, 0.15);