Question: [Website screenshot in PC](https://i.stack.imgur.com/UM5zY.png)

[Website screenshot in the mobile device](https://i.stack.imgur.com/ohFNd.png)

Here is the HTML code

```
<!DOCTYPE html>
<html lang="en">
<head>
  <link href="https://fonts.googleapis.com/css2?family=PT+Sans+Narrow:wght@700&display=swap" rel="stylesheet"
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <link rel="stylesheet" href = "boi.css">
</head>
<body>
  <div class="first">
    <h1>Hey!</h1>
</div>
</body>
</html>>

```

and this is the CSS code

```
body {
background-color: rgb(20, 18, 18);
}
.first {
    position: relative;
    margin-right: 300px;
    color: white;
        text-align: center;        
        font-family: 'PT Sans Narrow', sans-serif;
}

```

Answer: 
In case anyone else runs into the issue, in my case it was because I was passing the entire URL, i.e.

http://someurl/jenkins/computer/test/slave-agent.jnlp

and what it really wanted was

http://someurl/jenkins/
Set global environment variable **jenkins.agent.inboundUrl** to your private adderess (with http/https) + port + suffix (if set).

This value will be used as url in JNLP file. This enables using a private address for inbound tcp agents, separate from Jenkins root URL.

see: <https://issues.jenkins.io/browse/JENKINS-63222>