Accessing your Browser's Developers' Tools:
Opening the Developer Tool:
Chrome - Shift + CTRL + J (on Windows/Linux), or Option + ⌘ + J (on macOS).
Firefox - Ctrl + Shift + I or F12 (on Windows and Linux), or Cmd + Opt + I (on macOS).
The Developer Tools can also be accessed, on either Chrome or Firefox, by right-clicking the screen and selecting 'inspect'.
Check that the files are downloaded correctly.
Check to see if the files are being downloaded from the server or recalled from the cache and if there were any files that weren’t loaded correctly.
Check network timings: