when creating a form around input fields and setting the form background-color to black. It won´t apply unless I define a height for the form. It wont wrap around the inputs. Same goes for the well class of bootstrap. There is some kind of bug. Please help me. Thanks.
If parent element (in your case <form>) contains the only floated elements, it would collapse.
Here is the article with more information: http://css-tricks.com/all-about-floats/