Fairly sure it's a piece of plexiglass with a LED strip around the edges. Normally the light would more or less bounce around inside the glass or escape to ligh

Fairly sure it's a piece of plexiglass with a LED strip around the edges. Normally the light would more or less bounce around inside the glass or escape to light up the environment. If you write on it the light hits the writing instead, giving it this cool-looking glow.