This example shows how to set the width of FileBox to a percentage of its parent container.
<div class="easyui-panel" style="width:100%;max-width:400px;padding:30px 60px;">
<div style="margin-bottom:20px">
<input class="easyui-filebox" label="width: 100%" labelPosition="top" style="width:100%">
</div>
<div style="margin-bottom:20px">
<input class="easyui-filebox" label="width: 80%" labelPosition="top" style="width:80%">
</div>
</div>