Login Button-Color Change

What is the custom CSS for changing the color of the “login” button on by adding the code within the plugin?

Here is what I have so far, which blocks “back to blog” link and makes my logo show up nicely without being skewed. What do I add to change the color of the button? And, where do I add it? I am clumsy at coding the CSS for WordPres. Thanks.

#login h1 a {
width:228px;
height:200px;
background-size: 200px 151px;
margin:0 auto;
display:block; }
#backtoblog { display:none; }

http://wordpress.org/plugins/custom-login/