Chart Prompts

Restyle my chart in the "Retention Curves" style described below. Keep my data, chart type, title meaning and units; change only the presentation. Use the charting library this project already uses (plain SVG if there is none). If the library can't express a detail, draw it in a custom layer instead of dropping it. Measurements assume a 960 x 600 chart; scale them proportionally.

Mood: a late-night growth dashboard. Deep indigo, a fan of thin decay curves warming from faded lavender to a hot magenta newest cohort, and a tidy legend strip that doubles as a scorecard.

Colors (use these exact values):
- Canvas: #17123B (deep indigo), with a soft radial glow of #2A2066 at 70% opacity centered near the upper left (30%, 20%) fading to the canvas color.
- Series ramp: interpolate in RGB from #9C8FD8 (lavender, oldest) to #FF2E97 (magenta, newest) with t = (index / (count - 1)) ^ 1.4, so the older lines stay cool and only the latest turn hot.
- Gridlines: #3A3470. Zero baseline: #6A62A8. Primary text: #ECE8FF. Secondary text: #9C96C4. Legend panel: #1F1950 with a 1px #3A3470 border.

Typography (Google Fonts):
- Urbanist for words: title 34px 700 (-0.4px letter-spacing, #ECE8FF, stating the finding), subtitle 15.5px 500 #9C96C4, legend names 14px 600 (newest 800 in #ECE8FF), small uppercase headers 11 to 12px 800 with 1.4px tracking, notes 12 to 13px 500.
- Space Mono for every number: axis labels 11px #9C96C4 ("80%", "W4"), legend values 13px 700 (#ECE8FF; newest in magenta).

Layout:
- 56px left margin; title baseline y 64, subtitle y 94.
- Plot from x 76 to 700, y 150 to 520. A vertical legend strip panel from x 740 to 924 (184 x 394, rx 10, top at y 138) on the right.
- Source line at y 580.

Axes and grid:
- Dotted horizontal gridlines at every 10% (1px #3A3470, dash 1 on 5 off, round caps); a solid 1.2px #6A62A8 zero line. Y labels every 20%. X labels every 2 periods ("W0" ... "W12") 22px below the plot, and a small axis title ("Weeks since signup") right-aligned below them. No vertical gridlines, no axis lines.

Marks:
- Line chart: one smooth monotone curve per cohort, drawn oldest first. Older cohorts are 1.4px with opacity rising from 0.5 to 0.9 with recency; the newest is 3.2px solid magenta over a 7px magenta blur (stdDeviation 4, 25% opacity) glow. Mark the newest cohort's end with a r 4.5 magenta dot with a 2px canvas ring, and its week 8 value with a r 3.5 hollow ring.
- Bar chart: grouped vertical bars per period with one thin bar per cohort in the same ramp (newest magenta, full opacity; older at 0.5 to 0.9), 2px gaps, square tops, and the same legend strip.

Labels and annotation:
- Legend strip: header row "COHORT" left and "WEEK 8" right, a 1px divider, then one row per cohort, newest at the top, 40px apart: a 14 x 4 px rounded swatch (newest 18 x 6), the cohort name, and its week 8 value right-aligned in Space Mono. Footer note "Newest cohort in bold".
- Flat-line annotation: from the week where curves stabilize to the right edge, a faint white (4.5% opacity, rx 6) band covering the curves' range, a dotted 1px leader up to a 1.5px #ECE8FF horizontal rule, with "CURVES GO FLAT AFTER WEEK 6" above the rule and a computed claim below it ("Every cohort loses under 1.5 pts a week from here").

Avoid: a categorical rainbow, thick lines for old cohorts, dots on every point, solid gridlines, a legend floating inside the plot, and claims in the annotation that the data does not support.

When you're done, render the chart and check that the color ramp reads oldest-to-newest in the legend, the newest curve clearly sits on top, the legend week 8 values match the curves, and the annotation text does not touch any curve.