What are CSS Color Level 4 spaces (LCH, Oklch)?

Modern CSS introduces perceptual color spaces like LCH and Oklch, which map closely to human vision and allow access to larger gamuts.

Unlike RGB or HSL, LCH maintains uniform lightness across hues. Modifying the hue of yellow and blue in HSL changes perceived brightness. In LCH/Oklch, lightness is mathematically isolated, making dynamic theming and accessible contrasts significantly easier.