doc: improve kbd element rendering

* better vertical alignment with text
* slightly larger "key" size
* remove top light area (from box-shadow)

PR-URL: #35497
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api_assets/style.css

@@ -576,14 +576,14 @@ kbd {
   background-color: #eee;
   border-radius: 3px;
   border: 1px solid #b4b4b4;
-  box-shadow: 0 1px 1px rgba(0, 0, 0, .2), 0 2px 0 0 rgba(255, 255, 255, .7) inset;
+  box-shadow: 0 1px 1px rgba(0, 0, 0, .2);
   color: #333;
   display: inline-block;
   font-size: .85em;
   font-weight: 700;
-  line-height: 1;
   padding: 2px 4px;
   white-space: nowrap;
+  vertical-align: middle;
  }
 
 .changelog > summary {