dynamic rectangular or square div of any size which can be fitted into a fixed size div [closed]

function renderBox() {

  const width = document.getElementById('width').value;
  const height = document.getElementById('height').value;
  const box = document.getElementById('box');
  
  let scale = 1;
  
  while(true) {
      if (width <= (400 * scale) && height <= (200 * scale)) {
      break;
      }
      scale++;  
  }
  
  box.style.width = width / (400 * scale) * 100 + '%';
  box.style.height = height / (200 * scale) * 100 + '%';
  
  document.getElementById('top').innerText = (200 * scale) + "px";
  document.getElementById('end').innerText = (400 * scale) + "px";
  
}

.container {
  margin-top: 20px;
  width: 400px;
  height: 200px;
}

.frame {
  background-color:rgb(200,200,200);
  width: 100%;
  height: 100%;
}

.scale #start {
  float:left;
}

.scale #end {
  float:right;
}

.scale #top {
  position: absolute;
  top: 0px;
  left: 10px;
}

#box {
  background-color: red;
  position: relative;
  top: 100%;
  transform:translateY(-100%);
  left: 0;
}

<div class="container">
 <div class="frame">
    <div id='box'></div>
 </div>
 <div class="scale">
    <span id='top'>200px</span>
    <span id='start'>0px</span>
    <span id='end'>400px</span>
 </div>
</div>

<br><br>

width: <input type="number" id='width'> <br><br>
height: <input type="number" id='height'> <br><Br>
<button onclick='renderBox()'>Render</button>