Demo -> https://jsfiddle.net/xdsuozxf/
Safari still requires the -webkit-
prefix to use flexbox.
.row{_x000D_
box-sizing: border-box;_x000D_
display: -webkit-box;_x000D_
display: -webkit-flex;_x000D_
display: -ms-flexbox;_x000D_
display: flex;_x000D_
-webkit-flex: 0 1 auto;_x000D_
-ms-flex: 0 1 auto;_x000D_
flex: 0 1 auto;_x000D_
-webkit-box-orient: horizontal;_x000D_
-webkit-box-direction: normal;_x000D_
-webkit-flex-direction: row;_x000D_
-ms-flex-direction: row;_x000D_
flex-direction: row;_x000D_
-webkit-flex-wrap: wrap;_x000D_
-ms-flex-wrap: wrap;_x000D_
flex-wrap: wrap;_x000D_
}_x000D_
_x000D_
.col {_x000D_
background:red;_x000D_
border:1px solid black;_x000D_
_x000D_
-webkit-flex: 1 ;-ms-flex: 1 ;flex: 1 ;_x000D_
}
_x000D_
<div class="wrapper">_x000D_
_x000D_
<div class="content">_x000D_
<div class="row">_x000D_
<div class="col medium">_x000D_
<div class="box">_x000D_
work on safari browser _x000D_
</div>_x000D_
</div>_x000D_
<div class="col medium">_x000D_
<div class="box">_x000D_
work on safari browser _x000D_
work on safari browser _x000D_
work on safari browser _x000D_
work on safari browser _x000D_
work on safari browser _x000D_
</div>_x000D_
</div>_x000D_
<div class="col medium">_x000D_
<div class="box">_x000D_
work on safari browser _x000D_
work on safari browser _x000D_
work on safari browser _x000D_
work on safari browser _x000D_
work on safari browser _x000D_
work on safari browser work on safari browser _x000D_
work on safari browser _x000D_
</div>_x000D_
</div>_x000D_
</div> _x000D_
</div>_x000D_
</div>
_x000D_