custom.css

/*.w3-theme {color:#fff !important; background-color:#32CD32 !important}
.w3-theme-l5 {color:#fff !important; background-color:#333 !important}
.w3-padding-almostnone{padding-top:64px!important;padding-bottom:0px!important}*/

img{
    max-width: 100%;
    max-height: 100%;
    display: block; /* remove extra space below image */
}
.box{
    width: 250px;
    /* border: 5px solid black; */
}
.box.large{
    height: 300px;
}
.box.small{
    height: 50px;
}

.footer {
    height:100%; // Replace with the height your footer should be
    width: 100%; // Don't change
    background-image: none;
    background-repeat: repeat;
    background-attachment: scroll;
    background-position: 0 0;
    position: fixed;
    bottom: 0;
    left: 0;
}

html, body {
  height: 100%;
}
body {
  display: flex;
  flex-direction: column;
}
.content {
  flex: 1 0 auto;
}
.footer {
  flex-shrink: 0;
}