css border cut corners

div {
  background: #c00;
  /* fallback */
  background: -moz-linear-gradient(45deg, transparent 10px, #c00 10px), -moz-linear-gradient(135deg, transparent 10px, #c00 10px), -moz-linear-gradient(225deg, transparent 10px, #c00 10px), -moz-linear-gradient(315deg, transparent 10px, #c00 10px);
  background: -o-linear-gradient(45deg, transparent 10px, #c00 10px), -o-linear-gradient(135deg, transparent 10px, #c00 10px), -o-linear-gradient(225deg, transparent 10px, #c00 10px), -o-linear-gradient(315deg, transparent 10px, #c00 10px);
  background: -webkit-linear-gradient(45deg, transparent 10px, #c00 10px), -webkit-linear-gradient(135deg, transparent 10px, #c00 10px), -webkit-linear-gradient(225deg, transparent 10px, #c00 10px), -webkit-linear-gradient(315deg, transparent 10px, #c00 10px);
}

div {
  background-position: bottom left, bottom right, top right, top left;
  -moz-background-size: 50% 50%;
  -webkit-background-size: 50% 50%;
  background-size: 50% 50%;
  background-repeat: no-repeat;
}


/* Ignore the CSS from this point, it's just to make the demo more presentable */

div {
  float: left;
  width: 50px;
  margin: 15px auto;
  padding: 15px;
  color: white;
  line-height: 1.5;
}