How to decrease size of the border in CSS?

Question

I need to decrease size of my border-bottom similar to the first image. Can anybody help me?

How it can look like

How it actually looks like

Here's code:

 <section class="projects-section">
   <h2>These are some of my projects</h2>
 </section>

 .projects-section h2 {
  padding-top: 70px;
  color: #f0f0f0;
  font-size: 40px;
  font-family: "Raleway", sans-serif;
  text-align: center;
  border-bottom: 2px solid #f0f0f0;
 }