Add dark.css rules for ayop-logo.svg bricks and triangle

as requested by @MaPePeR in [this comment](https://github.com/deplicator/xkcdTime_atyourownpace/pull/141#issuecomment-23011943).
Can be viewed [here](http://code.lucaswerkmeister.de/xkcdTime_atyourownpace/index.html).