Center div on the middle of screen [duplicate]

Answer 1

Try this:

 div{
    position: absolute;
    top: 50%;
    left: 50%;
    margin-top: -50px;
    margin-left: -50px;
    width: 100px;
    height: 100px;
    background: red;
}

Here div is html tag. You wrote a html tag followed by a dot that is wrong.Only a class is written followed by dot.