body {
    box-sizing: border-box;
}
main {
    display: flex;
    flex-direction: column;
    align-items: center;
}
header {
    text-align: center;
}
.description {
    line-height: 20px;
    margin: 2em;
    max-width: 600px;;
}
.description ul {
    padding-left: 1em;
}
.description li {
    margin: 10px auto;
}
.container {
    display: flex;
}
.box {
    height: 4em;
    width: 4em;
    border: 1px solid black;
}
.red {
    background-color: red;
}