Your OC console\download CSS fonts from external sources. This may be the issue when your OC server does not have access to the internet.
Release : 20.3 - 20.4 CU4
It's an informational article.
This is what the webpage code looks like :
"
<html>
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<link rel="stylesheet" type="text/css" href="login.css">
<link rel="stylesheet" type="text/css" href="//fonts.googleapis.com/css?family=Open+Sans" /> !!!!<-------------------
</head>
<body>
<!--div style="text-align: right; padding-right: 10% ">
<h3>
<img src='/operatorconsole_portlet/key.png'/>
<a id="ssoUrl" href="#" rel="nofollow">Sign In</a> </h3>
"
the webpage is designed to request custom fonts from google fonts API. It's a popular technique. Here is the Google Fonts Api document for developers :
https://developers.google.com/fonts/docs/getting_started
In CU5 the webpage was redesigned and does not contain any external fonts anymore.