你說：
Use pure JavaScript code that creates a <main> element at the center of the visible screen. The <main> element always stays over other elements and occupies 1/4 area of the visible screen.
ChatGPT 說：

Here's a pure JavaScript solution to create a <main> element that stays centered in the visible screen and occupies 1/4th of the area. The <main> element will always stay over other elements as required.

html
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Centered Main Element</title>
  <style>
    body {
      margin: 0;
      padding: 0;
      height: 100vh;
      overflow: hidden;
    }
  </style>
</head>
<body>

<script>
  // Create the <main> element
  const mainElement = document.createElement('main');
  
  // Style the <main> element to stay centered and occupy 1/4 of the screen
  mainElement.style.position = 'fixed';
  mainElement.style.top = '50%';
  mainElement.style.left = '50%';
  mainElement.style.transform = 'translate(-50%, -50%)';
  mainElement.style.width = '50vw'; // 50% of the viewport width
  mainElement.style.height = '50vh'; // 50% of the viewport height
  mainElement.style.zIndex = '9999'; // Ensure it stays over other elements
  mainElement.style.backgroundColor = 'rgba(0, 0, 0, 0.5)'; // Just to make it visible
  
  // Append the <main> element to the body
  document.body.appendChild(mainElement);
  
  // Update the position of <main> element when window is resized
  window.addEventListener('resize', () => {
    mainElement.style.top = '50%';
    mainElement.style.left = '50%';
    mainElement.style.transform = 'translate(-50%, -50%)';
  });
</script>

</body>
</html>

Key Points:

  1. The <main> element is positioned using position: fixed, which keeps it at the center of the screen at all times.
  2. The top: 50% and left: 50% positions place the element's top-left corner at the center of the viewport, and transform: translate(-50%, -50%) shifts it back to the center.
  3. The width and height are set to 50vw and 50vh respectively, making the element occupy 1/4 of the screen.
  4. z-index: 9999 ensures the <main> element is on top of other content.
  5. The resize event listener ensures the <main> element remains properly positioned even when the window is resized.

This will make the <main> element remain at the center, occupying a quarter of the visible screen and stay above other content.


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