fix toc underline decoration

assets/sass/_theme/design-system/table_of_contents.sass

@@ -31,7 +31,6 @@
             padding-top: 0
             padding-bottom: 0
             line-height: calc(var(--header-height) - 1px)
-
     .toc
         flex: 1
         display: flex
@@ -187,7 +186,7 @@
                 display: block
                 text-decoration-color: transparent
                 &:hover
-                    text-decoration: underline
+                    text-decoration-color: $toc-color
         .active
             color: $toc-active-color
             pointer-events: none