I am making a WordPress theme. But I have a problem. style.css stylesheet is not loading in page.php contents. When I edit a post in wp editor and add <div class=w3-red"> <button class="w3-btn w3-red"> and more related codes. When I published a post, they are not showing on front-end. I think WordPress doesn't support the page style customization option with wp editor. I have also added my own style.css in header.php.
I am using w3.css stylesheet in my web root directory. style.css
<div class="w3-card w3-red"> Hello </div>
This code in not loading in frontend.