Multivalue Lookup on newform.aspx is too narrow.

I need to expand the width of the Multivalue Lookup on NewForm.aspx and EditForm.aspx.

This post titled "NewForme.aspx MultiValue Lookup Width Modification" indicates that it can be done by creating a new NewForm.aspx or via JavaScript, but doesn't explain how it can be done with either solution.

Just creating a newform.aspx resulted in no change.

I would appreciate either detailed JS code or a step by step using a new newform.aspx.

Thank You.