CSS mix-blend-mode and background-blend-mode properties allow designers to layer elements so their colours interact — multiply darkens, screen lightens, and difference creates striking inversions. This is often used for text over images, overlapping shapes, or hover effects.
Blend mode results depend entirely on the colours involved, so they require testing across different content. Readability can suffer if text blending reduces contrast too much, and performance may vary when blending many layers simultaneously on lower-end devices.