Changing the width of a textbox that you see in Edit Mode

rying to figure out how I would change the width of a textbox that we have under the Information tab in Edit Mode.

I've had a look at the rendered HTML and it looks like this:

<input name="ctl00$FullRegion$PC_60_1$EditForm$MetaTagDescription$ctl00" class="episize240" type="text" maxLength="255" value="home page meta description"/>

That class 'episize240' is in a file called system.css that I'm guessing I'm not supposed to edit. Even if I could edit it, the rendered tag contains no 'id' attribute so I'm not sure I could write a selector for it.

The property type behind this textbox is PropertyString, and I'm guessing that 'episize240' is the default css