Problem with iframe height adaptation in div

The webpage is divided into three parts: upper, middle and lower. The upper and lower heights are fixed and the middle height is adaptive. The middle part is divided into left and right parts. The left width is fixed and the right width is adaptive. Now the width and height of the right div are adaptive. There is an IFrame in the right div. Do you want the IFrame to adapt to the width and height of the outer div?

The problem that occurred when I made it myself was: when the width and height of ifame were set to 100%, the iframe would be squeezed out of the div and slide down to the bottom of the div. Then I tried a lot of things on the Internet but couldn't solve it, so I added something so that the situation wouldn't happen

The following is the js setting of my div

<span style="color: #008000;">//</span><span style="color: #008000;">window.onresize表示窗口触发时间的时候执行</span><span style="color: #008000;">
//</span><span style="color: #008000;">两个函数，用闭包包裹起来()()</span>
window.onload=<span style="color: #0000ff;">function</span><span style="color: #000000;">(){
    (window.onresize</span>=<span style="color: #0000ff;">function</span><span style="color: #000000;">(){
    </span><span style="color: #008000;">//</span><span style="color: #008000;">获取可见宽度</span>
    <span style="color: #0000ff;">var</span> width=document.documentElement.clientWidth-180<span style="color: #000000;">;//180为左边的div的大小
    </span><span style="color: #008000;">//</span><span style="color: #008000;">获取可见高度</span>
    <span style="color: #0000ff;">var</span> height=document.documentElement.clientHeight-80<span style="color: #000000;">;//80为头部的div的大小可自己修改
    
    </span><span style="color: #008000;">//</span><span style="color: #008000;">如果有宽度就给值，</span>
    <span style="color: #0000ff;">if</span>(width>=0<span style="color: #000000;">){
        document.getElementById(</span>'main').style.width=width+'px'<span style="color: #000000;">;
        
    }
    </span><span style="color: #0000ff;">if</span>(height>=0<span style="color: #000000;">){
        document.getElementById(</span>'sidebar').style.height=height+'px'<span style="color: #000000;">;
        document.getElementById(</span>'main').style.height=height+'px'<span style="color: #000000;">;
    }
})()};</span>

This is css

<span style="color: #800000;">html</span>{<span style="color: #ff0000;">
    overflow</span>:<span style="color: #0000ff;"> hidden</span>;
    <span style="color: #008000;">/*</span><span style="color: #008000;">火狐则会去除改变窗口大小时出现的白条这个bug</span><span style="color: #008000;">*/</span>
}

For reference only, don’t spray if you don’t like it.