background-color in css is not working when navigating from one form to another : <p>When I try to navigate from one form to another form, background-color in css is not working.</p>

<p>login_form_success.php</p>

<pre><code>&lt;div class="alert alert-success"&gt;Welcome &lt;?php echo $_SESSION['uname']; ?&gt;Signed in !&lt;/div&gt;
</code></pre>

<p>style.css</p>

<pre><code>.alert alert-success{
    background-color: greenyellow;
}
</code></pre>
