form display problem

Your themes css is the likely culprit here, can you provide a link to a live page containing the form in question so we can examine the css and suggest possible solutions.

Yes, it's inheriting from your theme. Your theme is setting a 42px font size for any span element inside the "post" container. You can add this to the end of your theme stylesheet and it should override that for your forms.

[css]
body .post .gform_wrapper span {
	font-size: 12px !important;
	line-height: 1.4em;
}

screenshot: http://i.imgur.com/bf52TIF.jpg

Your theme is adding a background image to the ul element so following Kevin's advice above try adding this to remove the background image from the gravity forms ul element

body .post .gform_wrapper ul {
     background-image: none;
}