Move the input box' padding to a wrapper element.
<style>
div.outer{ background: red; padding: 10px; }
div.inner { border: 1px solid #888; padding: 5px 10px; background: white; }
input { width: 100%; border: none }
</style>
<div class="outer">
<div class="inner">
<input/>
</div>
</div>
See example here: http://jsfiddle.net/L7wYD/1/