Some insight into the design bug: The user agent stylesheet(default style for elements that comes with the browser) contains 2 pixels of padding on both sides of <textarea> elements. The padding + 1 pixel border is 3 pixels on each side, or 6 pixels overall of unaccounted for width. Since the element is set to 100% width, it breaks out of it's container.

Setting the padding to 0px and removing the border will obviously fix this, but looks strange.
Fix:A couple things I can think of off the top of my head to add to the <textarea>'s styles that would fix this is
Code
/* 1: */
margin-left:-1px;
padding:0;
/* 2: (I prefer this style as it gives the text padding) */
width: 99%;
margin: 0 0 0 -1px;
padding: .5%;
This post was edited by AnimeFTW on Jul 31 2014 07:33pm