• PX is a specific unit of size, similar to the meter and centimeter used in ordinary times

  • Em is a multiple of font-size relative to its parent element

  • Rem is a multiple of font size relative to the root element in HTML

    <style>
        html {font-size: 100px; }div {font-size: 20px; }p {font-size: 2em; /* Font-size :40px */
        }
        p {font-size: 2rem; /* Font-size :20px */
        }
    </style>
</head>
<body>
    <div>
        <p>Hello World!</p>
    </div>
</body>
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