fontes.html

<!DOCTYPE html>
<html lang="pt-br">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Fontes</title>

    <style>
        body {
            display: flex;
            flex-direction: column;
            gap: 15px;
        }

        button {
            width: 30px;
            cursor: pointer;
        }

        span {
            font-size: 14px;
            color: rgb(94, 94, 94);
        }

        p {
            transition: 500ms;
        }
    </style>
</head>
<body>

    <h1>Fontes</h1>

    <div>
        <button onclick="aumentar()">A+</button>
        <span>(Aumentar fonte)</span>
    </div>
    <div>
        <button onclick="diminuir()">A-</button>
        <span>(Diminuir fonte)</span>
    </div>
    <p>Olá Mundo.</p>

    <script>
        let fonte = 16;
        function aumentar() {
            fonte += 2
            document.querySelector('p').style.fontSize = fonte + "px"
        }

        function diminuir() {
            fonte -= 2
            document.querySelector('p').style.fontSize = fonte + "px"
        }
    </script>
    
</body>
</html>