<style type="text/css">
  #file {
    display: -moz-box;
    display: -webkit-box;
    display: box;
    background-color: blue;
    width: 300px;
    height: 100px;
  }

  #but {
    -moz-box-flex: 2;
    -webkit-box-flex: 2;
    box-flex: 2;
    height: 100px;
    background-color: red;
    max-width: 400px;
    min-width: 400px;
  }

  #name {
    -moz-box-flex: 3;
    -webkit-box-flex: 3;
    box-flex: 3;
    height: 100px;
    background-color: green;
  }
</style>
<div id="file"><div id="but">Some text</div><div id="name">Some more text</div></div>