CSS - Text - Text area width 100% exceeds container

Text areas with width: 100%; will often appear to exceed the boundaries of the containing element.

The solution is to use the box-sizing declaration, and set it to border-box:

-webkit-box-sizing: border-box;
-moz-box-sizing: border-box;
-ms-box-sizing: border-box;
box-sizing: border-box;

NOTE: Each of the major vendors support a vendor-specific extension, in addition to the more-direct but as-yet largely unsupported CSS3 declaration.