Options->Offline Mode: Offline mode can be toggled with Options->Offline Mode. When in offline mode, CSS HTML Validator assumes there is no Internet connection and therefore the program will not try to perform functions that require Internet access, like link checking.
View->Other->Integrated Web Browser Controls: Check this option to enable the integrated web browser and its controls. If you don't use the integrated web browser then this can be left unchecked for a simplified interface and more editing room. In versions prior to 2019/v19, the integrated web browser controls were always available but now they are hidden by default.