CSS: Set border to half width

Question

Consider following:

...


.box{
    width:500px;
    border-bottom: 1px solid #ccc;
}

It will set the bot

Answer 1

css:
    display: block; 
    margin: 0 auto; 
    width: 50%; 
    padding-top: 20px; 
    border-bottom: 1px solid #000;