How checked checkbox can change div's z-index?

[lightship]

I have a span with paypal button. I must make this paypal button avialable for pressing only after user confirms TOS. For this i think to lay over the span with the paypal button another div with unchecked checkbox, opacity and z-index. The user checks the checkbox and the layed over div gets such a z-index, so the span with paypal button will be over it and can be pressed.I need something likeHTML\[code\]<div class="with_zindex"> <input type="checkbox??????????????????????????????"><span class="here_is_paypal_button"></span></div>???????????????????????????????????????????????\[/code\]CSS\[code\].with_zindex{background-color:#fafafa; opacity: .5; filter: alpha(opacity=50); -moz-opacity: .5;z-index:1000;}.with_zindex + input[type=checkbox]:checked {z-index:-1000;}\[/code\]But this don't work for me (there are only given first formattings, which are not chenged by checking / unchecking checkbox).I'm deeply thankful also for another solutions and advices for a rookie like me.thanks in advance and best regards