Build a centred elliptical gradient from #FFFFFF at 0% to #0F172A at 100%, then add one midpoint stop. The resulting three-stop declaration demonstrates the tool's insertion arithmetic, not an imported preset or a contrast-approved colour palette.
Set an ellipse at 50% 50%
Choose Radial, select Ellipse and set both centre coordinates to 50. Begin with only the two endpoint colours above, then press Add Stop once. It inserts position 50 and colour #878B95: the rounded channel averages are 135, 139 and 149. Do not replace that inserted colour for this fixture. With these three rows, the tool can reproduce the same output without depending on the preview's apparent brightness.
Check the radial output and box shape
Expected output: background-image: radial-gradient(ellipse at 50% 50%, #FFFFFF 0%, #878B95 50%, #0F172A 100%);. No angle token belongs in this radial declaration. Its omitted size uses CSS's farthest-corner default. A wide box and a square box therefore show different ellipse proportions with identical CSS. Changing Ellipse to Circle or moving the centre produces a different declaration, not a formatting-only change.
Verify the declaration in its real context
Keep a background-color fallback and save the CSS before reloading: palettes are not stored. Test the target browsers and sizes. Check text contrast across the visible gradient, not just one point; the preview certifies neither accessibility nor compatibility.