We will now change the style of the checkout steps, as shown in this screenshot:

We inspect the element, as shown in the following screenshot, and change the CSS as per our requirement:

Add the following CSS to the end of catalog/view/theme/packttheme/stylesheet/stylesheet.css and refresh the checkout steps. You will see the changes. You can see the canceled portion of CSS from bootstrap.min.css, which means that the bootstrap.min.css class is overridden by the stylesheet.css class:

.panel-default>.panel-heading {
  color: #fff;
  background-color:#e84e1b;
background-image: linear-gradient(to bottom, #e84e1b, #c93a17);
  background-repeat: repeat-x;
  border-color: #e84e1b;
}

The code has changed the step's heading to an orange background. In this way, you can make changes and implement them in your theme.