gradient border transparent inner
HTML
<div id="example">
<div id="cont">
<div id="box"></div>
</div>
</div>CSS
#cont{
background: -webkit-linear-gradient(left top, crimson 0%, #f90 100%);
width: 300px;
height: 300px;
border-radius: 1000px;
padding: 10px;
}
#box{
background: #fff;
width: 300px;
height: 300px;
border-radius: 1000px;
}
#example {
background: url(http://blogs.taz.de/hausblog/files/2017/12/20171208_FB_reuters2.png);
}