CSS смещенная граница
* {
box-sizing: border-box;
}
.container {
height: 200px;
width: 200px;
position: relative;
background-color: red;
margin: 20px;
}
.inner {
width: 100%;
height: 100%;
position: absolute;
border: 2px solid black;
top: -10px;
left: -10px;
z-index: 10;
}
Poor Piranha