In this exercise we are building a nice effect panel effect that will work great on a gallery. We make use of flexboxes.

The logic behind this exercise is very simple. We listen for two events:

• When there is a click in a panel, we toggle the .open class from the flex panel.

• And when the panel's transition ends(transitioned) we toggle the .open-active class from all the childs of the panel. It's worth mentioning how we filter the event, to get only the one that interests us:

   function toggleActive(e) {
     if(e.propertyName.includes('flex'))
        this.classList.toggle('open-active');
  }

Now the magic happens in the HTML and CSS code. So the templates structure is:

<div class="panels">
  <div class="panel panel1">
    <p>Hey</p>
    <p>Let's</p>
    <p>Dance</p>
  </div>
  <div class="panel panel2">
	...
</div>

And in the CSS:

• panels is used to define the flex-container. It is nice how he uses vh.

• panel here are defined the common properties as a flex box for all the flex-pannels as well as the background properties. It also contains the transition for which we listen in the JS:

   transition:
     font-size 0.7s cubic-bezier(0.61,-0.19, 0.7,-0.11),
     flex 0.7s cubic-bezier(0.61,-0.19, 0.7,-0.11),
     background 0.2s;

  Also we define that all children of the panel are going to have a transition effect, but later only the first and last will have this .open-active class:

   .panel > * {
     transition:transform 0.5s;
  }
  .panel > *:first-child { transform: translateY(-100%); }
  .panel.open-active > *:first-child { transform: translateY(0); }
  .panel > *:last-child { transform: translateY(100%); }
  .panel.open-active > *:last-child { transform: translateY(0); }

  And last but not least the effect to make bigger a panel comes from the flex properties:

  .panel.open {
     flex: 5;
     font-size:40px;
  }

• panelsX where x is between [1, 5] is how we define a particular background that each panel will have.

• click
• transitioned: when a CSS transition ends