Edit in JSFiddle

#esnekKutuKapsul {
     background: gray;
    border: blue;
    display: box;
    display: -webkit-box;
    display: -moz-box;
    display: -ms-box;
    width:600px;
}
.esnekKutu {
    background-color:#999999;
    height:150px;
      width:100px;
}
#esnekKutu1 {
    background-color:#0CF;  
    box-flex: 2;
    -webkit-box-flex: 2;
    -moz-box-flex: 2;
    -ms-box-flex: 2;
}
#esnekKutu2 {
    background: lightgray;
    box-flex: 1;
    -webkit-box-flex: 1;
    -moz-box-flex: 1;
    -ms-box-flex: 1;
}
#esnekKutu3 {
    background-color:#9C3;    
    box-flex: 1;
    -webkit-box-flex: 1;
    -moz-box-flex: 1;
    -ms-box-flex: 1;
}
<div id="esnekKutuKapsul">
    <div class="esnekKutu" id="esnekKutu1">Esnek Kutu1</div>
    <div class="esnekKutu" id="esnekKutu2">Esnek Kutu2</div>
    <div class="esnekKutu" id="esnekKutu3">Esnek Kutu3</div>
</div>