Kevin Flahaut's tips for css targeting specific elements not working on my check

Following the advice provided by Kevin Flahaut on this page: http://www.rocketgenius.com/gravity-forms-css-targeting-specific-elements/
I added the following code to my wordpress css:

[css]
/* gravity forms text field */
    body .gform_wrapper .gform_body .gform_fields .gfield input[type=text] { border:1px solid #dddddd; background-color:#f8f9fb; }

    /* gravity forms drop-down (select) field */
    body .gform_wrapper .gform_body .gform_fields .gfield select {border:1px solid #dddddd; background-color:#f8f9fb; }

    /* gravity forms textarea field */
    body .gform_wrapper .gform_body .gform_fields .gfield textarea {border:1px solid #dddddd; background-color:#f8f9fb; }

    /* gravity forms checkbox inputs */
    body .gform_wrapper .gform_body .gform_fields .gfield .gfield_checkbox li input[type=checkbox] {border:1px solid #aec1d2;}

It worked perfectly EXCEPT the checkbox inputs, as you can see here:

http://dev12.campaignadvantage.com/action/volunteer/

So I tried Kevin's original code example in my css, which should have made the checkbox input borders red, but it didn't. Could you please help me figure out why Kevin's code does not appear to be working for my checkbox inputs, even though its working perfectly for the other fields?

Thanks!

Thanks, Kevin!