Fix horizontal scrollbar height, closes #5728

src/definitions/globals/site.less

@@ -135,6 +135,7 @@ a:hover {
   body ::-webkit-scrollbar {
     -webkit-appearance: none;
     width: @customScrollbarWidth;
+    height: @customScrollbarHeight;
   }
   body ::-webkit-scrollbar-track {
     background: @trackBackground;

src/themes/default/globals/site.variables

@@ -146,6 +146,7 @@
 @useCustomScrollbars: true;
 
 @customScrollbarWidth: 10px;
+@customScrollbarHeight: 10px;
 
 @trackBackground: rgba(0, 0, 0, 0.1);
 @trackBorderRadius: 0px;