[Aetae]

Только ff:

<style>
div{
    background: linear-gradient(-15deg, 
        transparent 0,
        transparent 14px,
        #ddd 15px,
        #ddd 100%);
    width:100px;
    height:100px;
    position:relative;
    filter:url(#f3);
    resize:both;
    overflow: hidden;
}
div:after{
    content: "";
    display:block;
    background: linear-gradient(15deg, 
        transparent 0,
        transparent 14px,
        #f70 15px,
        #f70 100%);
    transform: rotate(-30deg);
    width:58px;
    height:15px;
    position:absolute;
    bottom:0;
    right:0;
}
</style>
<svg height="0" width="0">
  <defs>
    <filter id="f3" x="-0.2" y="-0.2" width="200%" height="200%" >
      <feOffset result="offOut" in="SourceAlpha" dx="3" dy="3" />
      <feGaussianBlur result="blurOut" in="offOut" stdDeviation="3" />
      <feBlend in="SourceGraphic" in2="blurOut" mode="normal" />
    </filter>
  </defs>
</svg> 
<div contenteditable="true">div</div>

Хз как в других браузерах добиться такой же простоты.)