HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <title>:empty whitespace</title>
  <style>
    body {
      font-family: Arial, sans-serif;
      margin: 16px;
      color: #0f172a;
    }

    .box {
      margin-bottom: 8px;
      min-height: 2rem;
      background: #f8fafc;
    }

    .box:empty {
      outline: 2px solid #16a34a;
    }
  </style>
</head>
<body>
  <!-- Matches :empty -->
  <div class="box"></div>

  <!-- Does NOT match — space inside -->
  <div class="box"> </div>

  <!-- Does NOT match — nested empty child -->
  <div class="box"><span></span></div>
</body>
</html>

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CSS :empty — whitespace pitfall