IE9 CSS hack doesn't work

Question

I'm trying to apply some css properties for IE9 only here is my css code:

:root ul li.open,
:root ul li.closed {
    list-style-position: outside \0/IE9;
    float:right \0/IE9;
    width:calc(100% - 20px) \0/IE9;

}

also, I tried to do it, like this:

:root ul li.open,
:root ul li.closed {
    list-style-position: outside\;
    float:right\;
    width:calc(100% - 20px)\;

}

and like this:

ul li.open,
ul li.closed {
    list-style-position: outside\9\0;
    float:right\9\0;
    width:calc(100% - 20px)\9\0;
}

what I missing?