Problems changing image height with CSS

I am trying to change the height of an image with CSS code however for some reason it doesn't seem to be working. I can change the width fine, but not the height. Is this the correct code?       

img.form-image {

        width : 68%;

          height: 10%;

    }

Could you try having the height as auto to see if that helps?

img.form-image {

        width : 68%;

        height: auto;

}

Please get back to us if the issue still persists. We will be happy to help. 

Thanks for that however I only want the width and height to change when viewing it on mobile devices, so having it automatic wouldn't work.

If you want to change the size of you image only on mobile devices you will have to use @media query. 

If you want to find out more about media query CSS codes targeting different devices, here’s one good source. http://stephen.io/mediaqueries/. 

For example you can use try with this CSS code:

@media screen and (min-width: 10px) and (max-width: 540px){

img.form-image {

          width : 68%;

          height: 10%;

    }

}

Hope this will help. Let us know if you need further assistance.