How to disable the resize grabber of <textarea>?

Just use resize: none

textarea {
   resize: none;
}

You can also decide to resize your textareas only horizontal or vertical, this way:

textarea { resize: vertical; }

textarea { resize: horizontal; }

Finally, resize: both enables the resize grabber.

<textarea style="resize:none" name="name" cols="num" rows="num"></textarea>

Just an example