you cannot make a widget out of css. you can only change its appearance.
In case you might want to make a new widget, you must first register a new widget at function.php and add a another code in the desired area where you want your widget to be located.
code for registering widget in function.php
'name' => __( 'Your Widget Name', 'theme' ),
'id' => 'div-id-for-widget',
'description' => __( 'Your Widget Name', 'theme' ),
'before_widget' => '',
'after_widget' => '',
'before_title' => '',
here is the code for the desired area
you can always modify the code to your liking
btw, nice site. only that there is a missing image in your header section. might be a logo or something.