how change an quarrel symbol settlement controlling css?

so, i emanate an quarrel symbol an settlement using

<input type="image" src="/images/btn.png" value="">

but, i can't same function controlling css. instance, i've tried

<input type="image" class="mybutton" value="">

where "mybutton" tangible css record as

.mybutton {
    background:url(/images/btn.png) no-repeat;
    cursor:pointer;
    width: 200px;
    height: 100px;
    border: none;
}

if that's i wanted do, i uncanny style, nonetheless i wish change button's coming float (using mybutton:hover class). i know links good, since i've means bucket credentials settlement tools page (just check). i found examples web controlling javascript, nonetheless i'm looking css solution.

i'm controlling firefox 3.0.3 creates difference.