<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>