section.banner {
    background-color: #F1F4F7;
    height: auto;
    margin: 0 auto;
    padding: 10px 8px 5px;
    position: relative;
    width: 1140px;
    z-index: 0;
}
#imgMedium, #imgSmall {
    display: none;
}
section.banner img {
   margin-bottom: -4px;
   width: 100%;
}
@media screen and (max-width: 1140px){ 
    section.banner {
        padding: 10px 0;
        width: 100%;
    }
}
@media screen and (max-width: 860px){
    #imgBig{
        display: none;
    }
    #imgMedium{
        display: block;
    }
}
@media screen and (max-width :450px){
    section.banner, section.banner img{
        width: 100%;
    }
    section.banner img{
        margin-left: 0px;
    }
    #imgMedium {
        display:none;
    }
    #imgSmall {
        display:block;
    }
}