Ok, let's try customize it together. But, first we have to know which widget we want to customize. In this example, I'll take widget called 'Label'.
Then I go to (after login to Blogger, off course) EditHTML and find widget called 'Label'.
Here, what I've got:
margin:10px 0 10px 0;
padding:8px 0 8px 10px;
font-family: Sans-serif, Arial, Helvetica;
color:#ffffff; text-shadow:0 1px 0 #fff;
I put my CSS on to template just above ]]></b:skin>. After I save it then I view my blog to find if it working or not.
Now, why don't you give it a try?