.portfolio {
    margin:  0;
    padding: 0;
    list-style: none;
    display:table;
    table-layout: fixed;
    width: 100%;
}

.portfolio__item {
    width: 100%;
    background-color: black;
}

@media screen and (min-width: 40em) {
.portfolio__item {
    display: table-cell;
    float: none;
    min-width: 20em;
    height: 20em;

}}

.portfolio__link {
    display: block;
    min-width: 20em;

}

.portfolio__link img {
    min-width: 20em;
    height: 20em;
    object-fit: cover;
    float: left;

}

.portfolio-nav {
    text-align: center;
    border-radius: 0;
    overflow: hidden;
}

.portfolio-nav a {
    text-decoration: none;
}

.portfolio-nav a:hover {
    opacity: 50%;
    background-color: black;
    transition: .5s ease;
}