how to define style in a css file code example

Example 1: external style sheet

<link rel="stylesheet" type="text/css" href="mystyle.css">

Example 2: start a css file

*{
    margin: 0;
    padding: 0;
    color: unset;
    box-sizing: border-box;
    text-decoration: none;
    outline: none;
    overflow-x: hidden;
}