Nice work. Just a couple tips about your UI:

#1— The background's fairly distracting. I'd either decrease its opacity, tone down the contrast, or switch to something like a colour/patterned background. You can also help things by adding a drop-shadow to the white text.

#2— Try to line things up & fix up the spacing. The "EARN" button is directly below the text-box, not lined up horizontally or vertically. There could be more space between "BTC Address:" and the box, which by the way looks disproportionately fat.

Other than that, great job; I like the nice & simple concept.