I made a powerpoint presentation & converted it to HTML at https://www.idrsolutions.com/online-powerpoint-to-html5-converter The output html page on the mentioned site looks perfect for me. But after I downloaded zip and put the contents on my new site (Ubuntu & PHP7 fresh install) I don't see the blue background. My site is https://castaneda.su/DK/221023 I tried to make these steps for my another site https://alpin52.ru/221023 (preconfigured by host provider) and the look is as required. I think the problem is that I missed installing some component on the server. But I cannot figure out which. Thanks.
I believe that's because you are missing HTTPS in the new domain so the browser is skipping some resources it considers insecure to load over non-HTTPS. Fix your HTTPS certificate situation and this problem should go away.
I used the inspect element to see the source code and saw that the div with the id (pg1Overlay) had the style
width: 100%;
height: 100%;
position: absolute;
z-index: 1;
background-color: rgba(0,0,0,0);
-webkit-user-select: none;
So, I changed it to
width: 100%;
height: 100%;
position: absolute;
z-index: 1;
background-color: blue;
-webkit-user-select: none;
and then the page was blue.