Not bad for a start, I do that the colors don’t mix well, try making a theme, and stick with that.
As for UIGradients on the buttons, I don’t think they work well. Try using different fonts as well.
For a first GUI, I think it’s amazing! However, the colors are pretty bad.
Here’s are the few fix I would do : change the buttons color, probably green. I’m not sure how you made the gui, but if you can keep the shadow on them and just change the color itself. Then, you should change the width of the Pad itself, it’s way too large. You should also change the background color of the Pad, I would suggest a darker color. You could also change the front of the buttons (front = style of the text, the calligraphy). The last thing, I’m not sure what is better, but you can put your X button outside of the pad, like at the same height and all, but just a bit at the right of the pad, or if you do as I suggested previously - reduce the width of the pad, you wouldn’t even need to move it, since I suggest you to reduce it between verification and “x” button.