Question

I got a requirement for text that looks like this:

Top shadow: 2px, #000, 75%

What does that mean? Is that just a text-shadow? What’s the 75% mean?

Answer 1

It is not valid text-shadow.

May be you need such example (with correct syntax):

text-shadow: 0 0 2px rgba(0, 0, 0, .75);

or

text-shadow: 0 2px 2px rgba(0, 0, 0, .75); /* down shadow */

Notes:
rgba(0, 0, 0, .75) = #000 with 75% opacity

Updates: @Xander found technique which you are asked us about. In it box-shadow with css generated content are using:

body:before {
    content: '';
    position: fixed;
    top: -1px;
    left: 0;
    width: 100%;
    height: 1px
    -webkit-box-shadow: 0 2px 2px rgba(0, 0, 0, .75);
            box-shadow: 0 2px 2px rgba(0, 0, 0, .75);
    z-index: 100;
}