ol {
    list-style-type: upper-roman;
    
    background-color: #DDD;
    border: 10px solid #BBB;
    border-top-left-radius: 25%;
    border-top-right-radius: 25%;
    padding: 2em;
    max-width: 40%;
    box-sizing: border-box;
    display: inline-block;
}

ol li {
    margin-right: 20%;
}

ol li:nth-child(even) {
    margin-left: 20%;
    margin-right: 0;
    direction: rtl;
}