Forum button style

This is one that has got me for some time and normally I just give up and toss in the too hard basket.

I have a form which has a style on it like:

.index_new input{
	border: 1px #000 solid;
	background-color:#fff;
}

But the thing I cannot work out is now with the button on the forum like this:

<input name="button" type="image" class="cont_but" id="button" src="../images/continue.png" />

and even another style for the button like this:

.cont_but{
	background-image:url(../images/continue.png);
	background-repeat:no-repeat;
	width:80px;
	height:24px;
}

I still cannot get rid of the input style on the button and it looks horrid.
Does anyone know the trick to this?

Ta muchly.