如何将我的代码从PHP更改为HTML?

I have some code for my website that does not host PHP properly. Switching to a PHP-compatible server is not an option. How can I change it to HTML?

index.php:

    <head>
        <link rel="stylesheet" type="text/css" href="CSS/index.css">
        <?php
        include("common/common.php")
        ?>
    </head>
    <body>
        <?php
            commonheader()
        ?>
        <h1>Coming Soon!</h1>

common.php:

<head>
    <link rel="stylesheet" type="text/css" href="common.css">
</head>
<?php
    function commonheader()
    {
        ?>
        <div class="header"
            <nav>
                <a href="index.php"><button type="button">Home</button></a>
                <!--First Case (unnamed)-->
                <button type="button"><span class="comingsoon">Coming soon!</span></button>
                <!--Second Case (unnamed)-->
                <button type="button"><span class="comingsoon">Coming soon!</span></button>
                <a href="help.php"><button type="button">Help</button></a>
            </nav>
        </div>
        <?php
    }
?>

If I need to attach CSS files, I can.

You just need to remove php code and only use html

    <head>
        <link rel="stylesheet" type="text/css" href="CSS/index.css">

    </head>
    <body>
        <div class="header">
            <nav>
                <a href="index.html"><button type="button">Home</button></a>
                <!--First Case (unnamed)-->
                <button type="button"><span class="comingsoon">Coming soon!</span></button>
                <!--Second Case (unnamed)-->
                <button type="button"><span class="comingsoon">Coming soon!</span></button>
                <a href="help.html"><button type="button">Help</button></a>
            </nav>
        </div>

        <h1>Coming Soon!</h1>