Improve language-switch CSS

Closes gh-23454

src/docs/asciidoc/css/stylesheet.css

 @import 'css/spring.css';
 
 .listingblock .switch {
-    border-width: 1px 1px 0 1px;
-    border-style: solid;
-    border-color: #282c34;
+    border-style: none;
     display: inline-block;
+    position: relative;
+    bottom: -3px;
 }
 
 .listingblock .switch--item {
@@ -13,15 +13,15 @@
     color: #282c34;
     display: inline-block;
     cursor: pointer;
+    border-top-left-radius: 4px;
+    border-top-right-radius: 4px;
 }
 
 .listingblock .switch--item:not(:first-child) {
-    border-width: 0 0 0 1px;
-    border-style: solid;
-    border-color: #282c34;
+    border-style: none;
 }
 
 .listingblock .switch--item.selected {
     background-color: #282c34;
     color: #e6e1dc;
-}
\ No newline at end of file
+}