FAQ checked; button image doesn't show

Hi,
Trying to insert an image for the submit button and found this in your FAQ:

If your image already has text on it, do it like this:
background:url(http://www.642weather.com/weather/images/bg-submit.png) no-repeat; width:50px; height:24px; padding:0px 0 4px 0; border:none; text-indent: -1000em; cursor:pointer;

So I uploaded the image to media library and added this css in Styles>Submit button:

background: url=http://localhost/ADG-test/wp-content/uploads/2015/02/ADG-button-submit1.png; no-repeat; width:100px; height:30px; border:none; text-indent: -1000em; cursor:pointer;

No image showing in the form…
Help me out please?

Thanks!
Nynke

https://ww.wp.xz.cn/plugins/si-contact-form/