2026-css-anchor-positioning/anchor-fallback.html at main · codegrid/2026-css-anchor-positioning · GitHub

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<!DOCTYPE html>
<html lang="ja">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <link rel="stylesheet" href="style.css">
  <title>アンカーが見つからない場合の代替値</title>
  <style>
    *, *::before, *::after {
      box-sizing: border-box;
    }

    body {
      margin: 0;
      font-family: sans-serif;
      min-height: 100vh;
      display: flex;
      align-items: center;
      justify-content: center;
      background-color: #f5f5f5;
    }

    .controls {
      position: fixed;
      top: 16px;
      left: 50%;
      translate: -50% 0;
      display: flex;
      align-items: center;
      gap: 12px;
      padding: 10px 16px;
      background-color: #fff;
      border: 1px solid #ddd;
      border-radius: 8px;
      font-size: 14px;
      z-index: 1;
    }

    .controls label {
      display: flex;
      align-items: center;
      gap: 6px;
      cursor: pointer;
      user-select: none;
    }

    .anchor {
      anchor-name: --my-anchor;
      padding: 12px 24px;
      background-color: #1a73e8;
      color: #fff;
      border-radius: 4px;
      font-size: 14px;
    }

    .anchor.is-hidden {
      display: none;
    }

    .target {
      position: absolute;
      position-anchor: --my-anchor;
      top: anchor(top, 100px);
      left: calc(anchor(right, 100px) + 10px);
      padding: 12px 24px;
      background-color: #6f42c1;
      color: #fff;
      border-radius: 4px;
      font-size: 14px;
      white-space: nowrap;
    }
  </style>
</head>
<body>
  <div class="controls">
    <label>
      <input type="checkbox" id="toggle">
      アンカー要素を非表示にする（<code>display: none</code>）
    </label>
  </div>

  <div class="anchor" id="anchor">アンカー要素</div>
  <div class="target">配置される要素</div>

  <script>
    document.getElementById('toggle').addEventListener('change', (e) => {
      document.getElementById('anchor').classList.toggle('is-hidden', e.target.checked);
    });
  </script>
</body>
</html>