WordPress File Upload – changed css, now input button not matching up

This is in regards to the plugin “WordPress File Upload” (which I could not find a support forum from the author, that’s why I’m writing this). I recently changed some of the plugin’s css, since for whatever reason none of my custom css in regards to that plugin was working. I changed some of the css rules from positioning: absolute to positioning: relative, which had the desired effect aesthetically, but now the input button (select box) is not working. It shows the click, but doesn’t open up the window that it should (it’s a button that lets a user upload files from their computer). If you click below it, then the desired window opens up. I’ve been playing around with this in Chrome, but I can’t figure out what I don’t have set correctly. I’m sort of a novice web designer, so basically I design out of necessity at work. Any help would be appreciated. The url to the page in question is https://www.fanemb.com/order/art-upload/ .