It is impossible to know for sure, but I've briefly reviewed the answers that you've given, and I think that I can see a pettern.
First, take a look at the questions that you are choosing to answer.
Several of them show very little effort from the questioner. One, for example, is about how to apply css to just one element on a page. That's the second thing covered by most css tutorials, and very easy to find on the web! Based on this lack of effort, I suspect that the questioner simply can't be bothered to upvote or accept your perfectly good answers.
Related to this, I suspect that the questions you've chosen don't attract much interest from other users. They're very much about the specific problem faced by a single user. If people aren't interested in the question, they probably aren't interested in the answers (yours or anyone else's) and so they don't upvote them. My evidence for this is that the questions themselves attract very few votes, and none of the other answers get many votes, either.
Second, look at your answers. They're fine, but not exceptional. Even a bad question can be rescued by a superb answer. And while there is nothing wrong with your answers (they're good, actually) they aren't going to make a name for you, either. For example, there was one about using css to make a particular shape of box. Your answer looks perfectly OK (I didn't test it). However, if you had included a couple of images, and a detailed explanation of your technique, some variations, and some ideas of other ways it could be used, then you might attract more up-votes (although, given the niche interest in this area, there are no guarantees).
One final observation: its nice to get recognition for your contributions, but if you're here primarily for the rep, you're probably here for the wrong reasons. For example, I don't expect to get much recognition for this answer, but I hope it will help you, and that makes it worthwhile for me. Moreover, answering this question has made me think, and that's good for me. Even if you don't like what I've said, and nobody else upvotes what I've written, then I still think it has been worthwhile answering.