This is a part of the geometry from my CSS FPS demo.
The lightmap is produced at 1/8th the scale of the plane. Scaling the lightmap down reduces the computation work required to create it (JavaScript) and keeps the texture small. When applied to an element, the lightmap is upscaled with background-size, triggering bi-linear filtering which softens the shadows. The multiply blend mode is then used to colour the underlying texture. The result is coloured lights :).
This demo also uses the vmin unit for the perspective so that it always fits the viewport