Q:

CSS - Shrink a background image to fit a div

I have the following CSS for a two-button voting system I am developing:
.upvote, .downvote {
    display: inline-block;

    width: 25px;
    height: 25px;
    border: 0;
    background-size: 100%;
    background-size: 25px auto;

    cursor: pointer;
    -webkit-touch-callout: none;
    -webkit-user-select: none;
    -khtml-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;
}
.upvote {
    background: url('./parts/icons/upvote.png');
}
.downvote {
    background: url('./parts/icons/downvote.png');
}

Also: 
<div class="upvote"></div>
<div class="downvote"></div>

The divs are set to a width and height of 25px, but the images upvote.png and downvote.png are much larger than that (128x128). I need to have the images shrink to 25x25 to fit the divs with CSS, but so far nothing is visible within the divs. 
If anyone can help me with this it would be appreciated. Thank you.

A:

Simply 
background-size: 100% 100%;

:)

