About blue-900
#1C398E is blue-900, a tailwind v4. This page shows its rgb(28, 57, 142) / hsl(224.74, 67.06%, 33.33%) / oklch(0.3796 0.1453 265.47) values, WCAG contrast against black and white, an OKLCH tint-and-shade ramp, and complementary, analogous, and triadic harmonies — all computed in perceptually-uniform OKLCH.