CSS underline less than width of headline? [duplicate]

Answer 1

Yes and no.

Normal borders cannot do this, but you can fake it with a CSS3 gradient border.

See: CSS3 Gradient Borders

Answer 2

You can use a pseudo element with :before (or :after):

h1 {
    font-weight: 300;
    display: inline-block;
    padding-bottom: 5px;
    position: relative;
}
h1:before{
    content: "";
    position: absolute;
    width: 50%;
    height: 1px;
    bottom: 0;
    left: 25%;
    border-bottom: 1px solid red;
}

http://jsfiddle.net/9e27b/