Box shadow

HTML

box-shadow: 20px 20px 5px 10px blue;
<div id="plus"></div>
<br>
<br>
box-shadow: 20px 20px 5px -10px blue;
<div id="moins"></div>

CSS

div {
    margin: 10px;
    padding: 10px; 
    background: lightblue;
    width: 120px;
    height: 120px;
}
#plus {
    box-shadow: 20px 20px 5px 10px blue;
}
#moins {
    box-shadow: 20px 20px 5px -10px blue;
}