w3schools border width code example

Example 1: border width css

.element {
  border-width: 2px;
}

Example 2: css border length

.page-title:after {
    content: ""; /* This is necessary for the pseudo element to work. */ 
    display: block; /* This will put the pseudo element on its own line. */
    margin: 0 auto; /* This will center the border. */
    width: 50%; /* Change this to whatever width you want. */
    padding-top: 20px; /* This creates some space between the element and the border. */
    border-bottom: 1px solid black; /* This creates the border. Replace black with whatever color you want. */
}