Responsive design is more than shrinking a desktop layout. A small screen changes how people read, navigate, and act.
Check the layout, not only the viewport
Test narrow screens for hidden grid tracks, fixed-width elements, clipped tabs, and unintentional horizontal scrolling. A layout can look fine at one width and still fail in between breakpoints.
Keep touch targets comfortable
Buttons, links, and controls need enough room to be tapped without precision. Make focus states visible for keyboard users too.
Respect user preferences
Support reduced motion, readable contrast, and scalable text. These are small implementation details with a large impact on usability.