title: Collapsible Panel in HTML/CSS
body: <p>I'm putting together a website. I need help creating the following feature: </p>
  
  <p>I want the "About" link to expand into a panel when clicked, and retract when the user presses "hide" in the panel. I've attached a diagram below to clarify what it should look like. When the user presses About in (1), it becomes (2), and when the user presses hide in (2), it becomes (1) again.</p>
  
  <p><img src="https://i.stack.imgur.com/xhPFE.png" alt="layout"></p>
  
  <p>I would like to do this in pure HTML/CSS, if possible. Does anyone know how I can do this?</p>