challenge.css

* {
    margin: 0;
    padding: 0;
}
nav {
    display: flex;
    justify-content: flex-start;
    width: 100%;
}

nav div{
    display:flex;
    justify-content: flex-end;
    align-items: center;
    width: 75%;
    background-color: black;
}

main {
    display: flex;
    justify-content: space-between;
    align-items: stretch;
    width: 95%;
    margin: 25px auto;
}

.green_link {
    background-color: green;
    color: white;
    padding: 20px;
    width: 25%;
}

.green_link:hover {
    color: #1182EB;
    background-color: black;
}

.black_link {
    background-color: black;
    color: white;
    padding: 0 20px;
    width: 200px;
    text-align: right;
}

.black_link:hover {
    color: #1182EB;
    background-color: white;
}

.panel_list{
    width: 60%;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
}

.right_panel {
    width: 40%;
    border: 3px solid black ;
    padding: 20px;
    margin: 15px;
}

panel {
    list-style: none;
    border: 3px solid black ;
    padding: 20px;
    margin: 15px;
    display: flex;
}

.distribution_space_between {
    justify-content: space-between;
}

.distribution_flex_end {
    justify-content: flex-end;
}

.distribution_flex_start {
    justify-content: flex-start;
}

cube {
    display: block;
    background-color: black;
    color: beige;
    width: 100px;
    height: 100px;
    margin: 0px 20px;
}