While I was working on the Sending mail from asp.net application, i have taken the text box of mail body, with multi line property. But when it is shown in browser, its size is changing when we drag its end point. So in order to fix that problem, by browsing on net i have found the simple CSS to fix the size of multi line text box .
To do this include the following code in your CSS file:

And you can use this style in your textbox by adding CssClass=”txtnoresize”.