JSFiddle - React, Tailwind, and code Playground

HTML

<h1 class="style1">My main page</h1>

<div id="embeddedPage">
    <!DOCTYPE html>
    <html>
        
        <head>
            <style>
                .style1 {
                    color: #0000ff;
                }
            </style>
        </head>
        
        <body>
     <?php
    require('page1.html');
       ?>
            

        </body>
    
    </html>
</div>

CSS

.style1 {
    color: #ff0000;
}