Here's a generic example:

    css // Begin CSS

    ( "selector1" )
    ({
        property1: value,
        property2: value,
        // ...
    })

    ( "selector2" )
    ({
        property1: value,
        property2: value,
        // ...
    })

    ; // End CSS

    // Variable
    var text_color = "black";

    // Mixin
    var dim = function( w, h ) {
        return {
            width:  w,
            height: h,
        }
    };

    css // Begin CSS

    ( "div" )( dim( "10px", "10px" ) )
    ({
        color: text_color,
    })

    ( "span" )
    ({
        color: text_color,
    })

    ; // End CSS

    item_color_input.onsubmit = function( )
    {
        css // Begin CSS

        ( ".item" )
        ({
            background: item_color_input.value,
        })

        ; // End CSS
    }

The Code: css.js http://keithmajhor.pastebin.com/twCKCcHV

    // ==============================================
    // File:   css.js
    // Author: Keith Majhor <[email protected]>
    // ==============================================
    window.css = function( a )
    {
        var decl = { },
            elem = { },
            rule,
            prop;

        css = function( a )
        {
            if ( typeof( a ) === "string" )
            {
                rule = a;
                if ( !decl[rule] )
                {
                    decl[rule] = { };
                    elem[rule] = document.createElement( "style" );
                    document.head.appendChild( elem[rule] );
                }
            }
            else if ( rule )
            {
                for ( prop in a )
                    decl[rule][prop] = a[prop];

                var temp = rule + "{";
                for ( prop in decl[rule] )
                    temp += prop + ":" + decl[rule][prop] + ";";
                elem[rule].innerHTML = temp + "}";
            }

            return css;
        }

        return css( a );
    }

I hope this is useful to someone. If anyone has any insight into why this might be a really stupid thing to do, I'd love to hear it.