@hsandt Hey. Is #box the body element? The body is always absolutely positioned, so in that case use height: auto; top: 0; bottom: 80dp;. I think that should do it.
If it's not the body, you can use position: absolute; together with the above rules.
@giulio.camuffo:matrix.org I have a SDL2Renderer Rml interface that does not require GL. Welcome to try it out.. working on everything except android at the moment. Still working on that. https://github.com/aquawicket/SDL2RendererRml