Clicking on the “Edit Forms CSS file” Quick link will redirect you to the page where you can edit the the colors, size, fonts (etc) of the search forms, add forms, etc.
CSS - Cascading Style Sheets. For more information about 'CSS' see the http://en.wikipedia.org/wiki/Css
On the top of the opened page you will see the locations of the file(s) you’re going to edit:
Under that you can see the wide text area containing the code you can edit:
For example you may need to enlarge the size of all text fields. Then you need to find the following part of the form.css file code:
border:1px solid #C6C6C6; - this is the edging of the text field, its border. Width is 1px and color is C6C6C6
width:313px; - And this is the width of the text fields which you can modify the way you need.
After you finished editing the code, make sure to press the “Save” button to submit the changes.
You can find more instructions and examples for basic design customizations in the "Tutorial" section of the Manual.