fix: Fix oblong collapse/expand button appearance on mobile safari

Author: fritz-c

src/node-renderer-default.scss

@@ -212,6 +212,7 @@ $row-padding: 10px;
   box-shadow: 0 0 0 1px #000;
   width: 16px;
   height: 16px;
+  padding: 0;
   top: 50%;
   transform: translate(-50%, -50%);
   cursor: pointer;