Classic responsive design cuts the web into steps: a mobile version, a tablet one, a desktop one. In between, the site jumps from one stair to the next. Text that suddenly grows, a grid that reorganises abruptly. What you actually maintain is three layouts. And three chances to break something.
Fluid, or continuous
A fluid site has no versions. It adapts continuously, from the smallest screen to the largest, with no stairs. Text, margins and images grow together, at the right speed. clamp() and container queries made that possible without JavaScript. It is not three well-tuned sites. It is one site that breathes.
What the eye does not see but feels
Good fluid work goes unnoticed, and that is the point. No jump betrays a change of format, no area breaks at a forgotten width. On any phone, tablet or work screen, the proportions stay right. Nobody will ever congratulate this work, since it consists precisely in there being nothing to notice. I still hold it to be the strongest UX there is: you stop thinking about the device, you read.
Less code, better holding
Three mockups means three times the design, build and testing work. One fluid scale, set once, covers the whole range. Fewer breakpoints, fewer rules, fewer edge cases dragging bugs along for years. Fluid is not only nicer to live with. It is simpler to hold over time.
Three versions means three times the risk. A single fluid one is better to live with and safer to maintain. EVA CSS turns it into a method.
