How do I make sure my site works on every device and browser? — answered by Engineer Saeed Baatiah
Do not test on your own device alone — that is the most common reason faults are discovered by customers. Test on at least four cases: a recent iPhone, a mid-range Android rather than a flagship, a tablet, and a large desktop screen. Add a test on a slow network, and with the system font size increased. A mid-range device on a slow network is the truest test, because it represents the majority of your actual visitors.