How can I make a TextArea 100% width without overflowing when padding is present in CSS?

Question

I have the following CSS and HTML snippet being rendered.

<

Answer 1

How about negative margins?

textarea {
    border:1px solid #999999;
    width:100%;
    margin:5px -4px; /* 4px = border+padding on one side */
    padding:3px;
}