Mobile-first with min-width
Level 1 of 10Your goal
Keep the box 200px wide by default, but make it 400px wide when the viewport is at least 600px wide. Expected: 200px on the 420px stage, 400px on the 700px stage. The height stays 80px.
Checked at 2 stage widths (420px, 700px) — every stage below has to match.
stage 420px
stage 700px
target content boxtarget outer edge (green = matched, red = not yet)
Feedback updates as you type, and your CSS is saved in this browser. Exact target numbers are in the Target panel.