.flexslider {
    width: 100%;
     height: auto;
     margin: 0 0 20px;
 }

 .flexslider .slides img {
     max-height: 300px; /*maximum height for all slides*/
     width: auto; /*proper aspect ratio of images*/
     max-width: 100%; /*maximum width for all slides*/
     margin: 0 auto; /*centering images in the container*/
 }

 @media only screen and (max-width: 480px) {
    .flexslider .slides img {
        max-height: 150px; 
    }
 }