Transparent borders

see: http://theamazingweb.net/2012/10/17/how-to-make-a-transparent-border-in-css/

by Jens Grochtdreis

HTML

<div class="box outside-border"></div>

<div class="box inside-border"></div>

CSS

html {  padding: 20px 0; background-color: #efefef;}
body {  width: 80%; 
        padding: 40px; margin: 0 auto; 
        background: #fff; 
        box-shadow: 1px 1px 5px rgba(0,0,0,0.5); 
        font-family: Verdana, Arial, sans-serif; 
        font-size: 14px;}

.box {
    margin: 0 auto 40px auto;
    width: 300px;
    height: 120px;
    background: #529db5;
}

.outside-border {box-shadow: 0 0 0 10px rgba(0,0,0,0.3);}

.inside-border {box-shadow: inset 0 0 0 10px rgba(0,0,0,0.3); }