Any CSS declarations need to be added between the <style type="text/css"> </style> tags, for exmaple:
background:none repeat scroll 0 0 #DDEEEE;
border:1px solid #000000;
In order to change the background color of the input fields you will need to go to the Components tab, edit your desired field and add the following lines in the Additional attributes property
You can read a detailed example on how to add a tooltip to your form fields here.