How to change a tag to button tag?

because I am connected to facebook, I will need the following functions:

$loginUrl = $helper->getLoginUrl("https://xxx.xxx.com/fb-sdk/fb-callback.php", $permissions);

        echo "<a class="user_signup_btn_facebook" href="" . htmlspecialchars($loginUrl) . "">Facebook</a>";

but what he proposes htmlspecialchars ($loginUrl) is the a tag
which will lead to my class user_signup_btn_facebook this perfect
which he will only do on button will be completely dropped when a tag is implemented!
how can I change this a header to a button header and issue htmlspecialchars ($loginUrl) in the same way?

Button css3 html5 php7 php

Mar.14,2021

echo '<button class="user_signup_btn_facebook" onclick="' . htmlspecialchars($loginUrl) . '">Facebook</button>';

how about this

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