fix: hide textarea scrollbar when content doesn't overflow

Set overflow-y: auto on textarea so the vertical scrollbar only
appears when content exceeds max-height. Fixes #43.

src/index.css

@@ -46,6 +46,7 @@ textarea::-webkit-scrollbar-thumb:hover {
 
 textarea {
   overflow-x: hidden;
+  overflow-y: auto;
   overflow-wrap: break-word;
   word-break: break-word;
 }