As you can see in the screenshot, classes are not showing in browsers. Also div with classes are not showing. Is it not possible to add classes in Announcements? I am using Text Editor Extras to have the possibility to add HTML code in TinyMice for Announcements.
TinyMCE strips out most tags that wouldn’t be used as part of the options that are part of TinyMCE. You can see an explanation of this here: Adding images to announcements in OJS 3.3 - Tiny MCE - #4 by rcgillis - the same principle applies - if you’ve added additional HTML, it would likely be stripped out.