a:link{
    transition: color 0.5s;
}


#html_logo {
    opacity: 0.25;
    transition: opacity 1s;
}

#html_logo:hover {
    opacity: 1;
}






figure {
    position: relative;
}

figure img {
    position : absolute;
    top: 0;
    left: 0;
}

figure .visible {
    opacity: 1;
    transition: opacity 0.5s;
}

figure .hidden {
    opacity: 0;
}


figure:hover .hidden {
    opacity: 1;
}

figure:hover .visible {
    opacity: 0;
}