Garbled pages can be a problem with your browser, or the server holding the page, or your internet connection, or something else entirely. After trying a quick refresh your first bit of detective work should be to load up the page in another browser on another device if possible, which will tell you whether or not the issue is at your end.
Another tell-tale sign is whether or not the problem is restricted to one site or many sites. If it’s the latter, it’s more likely something is going wrong with your browser, or your internet connection isn’t doing its job properly (quickly switching to a different browser should help you decide whether it’s the former or the latter).
If you manage to narrow down the source of the problem to your browser, try clearing the local file cache, as we described in tip 1 above—this will force the program to reload everything on the page and should fix the issue. If not, systematically disabling extensions one by one (see tip 1), or uninstalling and reinstalling your browser are usually enough to get everything working properly again.