css-units/rem.html at main · codewithgui/css-units · GitHub

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<!doctype html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>REM Unit</title>
    <style>
      html {
        font-size: 16px;
      }
      body {
        font-family: sans-serif;
        padding: 20px;
        background: #f5f5f5;
      }
      h2 {
        font-size: 18px;
        margin-bottom: 12px;
        color: #333;
      }
      .box {
        font-size: 20px;
        background: #e0eaff;
        padding: 2rem;
        border-radius: 6px;
        margin-bottom: 12px;
      }
      .inner {
        font-size: 1.5rem;
        background: #4f8ef7;
        color: white;
        padding: 1rem;
        border-radius: 4px;
      }
      p {
        font-size: 13px;
        color: #666;
        margin-top: 8px;
      }
    </style>
  </head>
  <body>
    <h2>rem — Always relative to root (html)</h2>
    <div class="box">
      Parent has font-size: 20px — but padding uses rem
      <div class="inner">1.5rem = 24px no matter what the parent says</div>
    </div>
    <p>rem always refers to the root html font-size (16px by default).</p>
    <p>No compounding — predictable everywhere in your project.</p>
  </body>
</html>