Your browser has a folder in which certain items that have been downloaded are stored for future use. Graphic images (such as buttons and icons), photo's, and even entire web pages are examples of items which are saved or cached. When visiting a webpage your browser checks if a copy of the files on the page is in its cache already. If so, it will save the visitor some downloading and make webpages load faster. Some browsers refer to it's cache as Temporary Internet Files.
This website sends instructions to your browser NOT to cache pages but unfortunately sometimes browsers choose to ignore that request and that can result in old files being served behind the scenes. One prime example of that problem is with "css style sheets". If your computer or device has cached an old copy it may need the new version.
If you are facing a problem and think it is due to browser cache issues, you should first try the browser’s incognito/private mode. And, if you still see the problem, it is not your cache, it is something else.
A hard refresh is a way of clearing the browser’s cache for a specific page, to force it to load the most recent version of a page. Sometimes, when changes are made to the website, they don’t register immediately due to caching. A hard refresh will usually fix this, though occasionally completely clearing the cache is necessary.
I am unable to fully test Opera and Vivaldi on any other operating system.