How it works
Responsive design adapts a layout to the available space and input conditions. Fluid widths, flexible media and selected breakpoints work together. It also requires readable text, usable controls and sensible content order. Shrinking a desktop screenshot onto a phone is not a responsive interface.
A realistic example
A two-column term hero can become a single column on a phone, keeping the definition before the illustration. A wide comparison table may use a labelled scroll area instead of squeezing every cell into unreadable text. The information remains available while the presentation changes.
What to check
Test narrow widths, large text, landscape and keyboard navigation. Look for horizontal page overflow, cropped controls and unexpectedly large empty areas. Check image dimensions and source selection so that the browser loads a suitable image without changing the intended quality or aspect ratio.
Limits and next steps
Breakpoints should follow where content needs a different layout, not a fixed list of phone models. Do not remove essential explanations or actions on mobile. Test touch and pointer use, because a layout that fits the screen can still have unusable interaction targets.