because the document's frame is sandboxed and the 'allow-scripts' permission is not set
<p>I wrote a program that generated an html file with this header:</p>

<p><a href="https://i.stack.imgur.com/CMzrJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/CMzrJ.png" alt="enter image description here"></a></p>

<p>but I don't have <code>iframe</code> at all, let alone in sandbox</p>

<p><a href="https://i.stack.imgur.com/9lSrJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9lSrJ.png" alt="enter image description here"></a></p>

<p>When I open the page in the browser (hosted on a Jenkins server) I see no css.</p>

<p>These are the errors (security policy)</p>

<p><a href="https://i.stack.imgur.com/R7FUm.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/R7FUm.png" alt="enter image description here"></a></p>

<p>I have seen some posts on stockoverflow, saying the <code>&lt;meta&gt;</code> should be like:</p>

<pre><code>&lt;meta http-equiv="content-type" content="text/html; charset=utf-8 ;"&gt;
&lt;meta http-equiv="Content-Security-Policy" content="script-src 'self' http://onlineerp.solution.quebec 'unsafe-inline' 'unsafe-eval'; style-src 'self' maxcdn.bootstrapcdn.com"&gt; 
</code></pre>

<p>but as you can see in my print screen that didn't help</p>

<p>any idea, how can I fix this?</p>