This Tab Link item has the Current state by default, which means it has an extra class called .w--current declared in its HTML tag.
<a class="new-tab-link w--current"></a>
This description paragraph is hidden by default using display:none. It's only shown when the Tab Link element gets the Current state, once it's clicked.
I'm the content of Tab One
I'm the content of Tab Two
I'm the content of Tab Three
Double click the code Embed Component below in Designer mode to check the CSS custom code used in this demo.