我需要帮助将黄色框垂直居中。
<html>
<head>
<title></title>
</head>
<body style="border-collapse: collapse;">
<div style="margin: 100px; width: 100px; height: 200px; background-color: gray; border: 1px solid gray;">
<table style='background-color: white; width: 100%; height: 100%; border-collapse: collapse; vertical-align: top;'>
<tr>
<td style='height: 33.33%;'>
<div style="position: relative; width: 100%; height: 100%;">
<div style="position: absolute; top: -50%; height: 100%; display: table-cell; vertical-align: middle;">
<div style="border: 1px solid #ccc; width: 30px; height: 30px; background-color: yellow; ">A</div>
</div>
<div style="position: absolute; bottom: -50%; height: 100%; display: table-cell; vertical-align: middle;">
<div style="border: 1px solid #ccc; width: 30px; height: 30px; background-color: yellow; ">B</div>
</div>
</div>
</td>
</tr>
<tr>
<td style="height: 33.33%;">
<div style="position: relative; width: 100%; height: 100%;">
<div style="position: absolute; bottom: -50%; height: 100%; display: table-cell; vertical-align: middle;">
<div style="border: 1px solid #ccc; width: 30px; height: 30px; background-color: yellow; ">C</div>
</div>
</div>
</td>
</tr>
<tr>
<td style="height: 33.33%;">
<div style="position: relative; width: 100%; height: 100%;">
<div style="position: absolute; bottom: -50%; height: 100%; display: table-cell; vertical-align: middle;">
<div style="border: 1px solid #ccc; width: 30px; height: 30px; background-color: yellow; ">D</div>
</div>
</div>
</td>
</tr>
</table>
</div>
</body>
</html>