Hey Debbie!
You can create your own offline page.
Check this documentation: https://docs.mendix.com/howto/front-end/custom-error-page/?_gl=1*8xta1e*_ga*OTkyOTQ0MTE3LjE3MDA1NjA2OTQ.*_ga_4PE2C4QFC7*MTcwMDY0ODkyNS4zLjEuMTcwMDY1MDE1Ny4xMC4wLjA.
Kind regards.