如何设置div以填充动态大小元素占用的剩余位置

I have this code:

我有这个代码:

<div id="body" style="height: 295px; width: 427px; position: absolute; top: 261px; left: 284px;">

   <div id="header">
        Some dynamic text<br/>
        Some dynamic text<br/>
   </div>

    <div id="Content"> 
        <textarea id="text" style="width: 100%"> </textarea>

        <input type="file" style="width: 100%">
    </div>

   <div>
</div>
<div id="body" st