I can't resize an img!

I have tried many attempts to resize a gif and img but nothing is working. Here is my code:

<div class='banner' id="product-intro"><img class='img-setion' src ="img/headset_blackbg.gif"></div>
.banner {
    width: 90%;
    left: 0px;
    right: 0px;

    .img-section {
        width: 60%;
        left: 0px;
        right: 0px;
    }

}

Yes, I’m also SCSS. Can someone tell me what’s wrong?

left and right only work with absolute/relative positioning.