How would you build a responsive layout without detecting specific device names?

Start with content that works in a narrow viewport, flexible sizing, and semantic document order. Use flexbox or grid and introduce breakpoints where the content needs a different arrangement rather than targeting particular phones. Ensure images can shrink, long text wraps appropriately, and controls remain usable with zoom and keyboard navigation. Test several viewport widths and orientations, including intermediate sizes. Responsive design is not only rearranging columns; loading cost, readable typography, touch targets, and preservation of meaningful content also affect the experience.