Textarea width limit

I am using version: 3.1.8.2. and my site is still under construction. I am very happy with the ability to configure so many aspects of this contact form including background, text colour and even the text colour on the Submit and Reset buttons. The only thing I couldn’t change was the attachment button, which is no fault of this plug-in. I am using the Twenty Eleven theme with no sidebars, which allows a very wide contact form. After a lot of adding and removing width values, I have ended up with CSS style for form DIV: set at width:99%; margin-left:auto; margin-right:auto;, which looks ok even on a mobile. The Textarea width fills up the space between the borders with a little wider right margin. With various other width settings the Input Textarea Field Cols: settings seemed to have no effect. I have two questions: Firstly, what is a ‘col’ width and how does it relate to a px or character width? Secondly, I find that the Textarea can be dragged (pushing the border too) to the right-hand edge of the page. Is there any way to fix or limit the Textarea width to prevent this?