Div has no height even if it has content [duplicate]

See the Demo here . Just add overflow: auto; to your main container.

#gallery {
    border: 1px solid;
    border-radius: 10px 10px 10px 10px;
    box-shadow: 0 0 15px rgba(50, 50, 50, 0.7) inset;
    height: auto;
    margin-top: 20px;
    padding: 15px;
    overflow: auto;
}