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HTML

              
                <body>
  <nav class="main-navigation">
    <ul class="league-list">
      <li class="league">
        <button class="list-toggle js-list-toggle">American League</button>
        <ul class="division-list" aria-expanded="false">
          <li class="division">
            <button class="list-toggle js-list-toggle">East</button>
            <ul class="team-list" aria-expanded="false">
              <li class="team">
                <a href="orioles.html">Baltimore Orioles</a>
              </li>
              <li class="team">
                <a href="redsox.html">Boston Red Sox</a>
              </li>
              <li class="team">
                <a href="yankees.html">New York Yankees</a>
              </li>
              <li class="team">
                <a href="rays.html">Tampa Bay Rays</a>
              </li>
              <li class="team">
                <a href="bluejays.html">Toronto Blue Jays</a>
              </li>
            </ul>
          </li>
          <li class="division">
            <button class="list-toggle js-list-toggle">Central</button>
            <ul class="team-list" aria-expanded="false">
              <li class="team">
                <a href="whitesox.html">Chicago White Sox</a>
              </li>
              <li class="team">
                <a href="indians.html">Cleveland Indians</a>
              </li>
              <li class="team">
                <a href="tigers.html">Detroit Tigers</a>
              </li>
              <li class="team">
                <a href="royals.html">Kansas City Royals</a>
              </li>
              <li class="team">
                <a href="twins.html">Minnesota Twins</a>
              </li>
            </ul>
          </li>
          <li class="division">
            <button class="list-toggle js-list-toggle">West</button>
            <ul class="team-list" aria-expanded="false">
              <li class="team">
                <a href="astros.html">Houston Astros</a>
              </li>
              <li class="team">
                <a href="angels.html">Los Angeles Angels</a>
              </li>
              <li class="team">
                <a href="as.html">Oakland A&rsquo;s</a>
              </li>
              <li class="team">
                <a href="mariners.html">Seattle Mariners</a>
              </li>
              <li class="team">
                <a href="rangers.html">Texas Rangers</a>
              </li>
            </ul>
          </li>
        </ul>
      </li>
      <li class="league">
        <button class="list-toggle js-list-toggle">National League</button>
        <ul class="division-list" aria-expanded="false">
          <li class="division">
            <button class="list-toggle js-list-toggle">East</button>
            <ul class="team-list" aria-expanded="false">
              <li class="team">
                <a href="braves.html">Atlanta Braves</a>
              </li>
              <li class="team">
                <a href="marlins.html">Miami Marlins</a>
              </li>
              <li class="team">
                <a href="mets.html">New York Mets</a>
              </li>
              <li class="team">
                <a href="phillies.html">Philadelphia Phillies</a>
              </li>
              <li class="team">
                <a href="nationals.html">Washington Nationals</a>
              </li>
            </ul>
          </li>
          <li class="division">
            <button class="list-toggle js-list-toggle">Central</button>
            <ul class="team-list" aria-expanded="false">
              <li class="team">
                <a href="cubs.html">Chicago Cubs</a>
              </li>
              <li class="team">
                <a href="reds.html">Cincinnati Reds</a>
              </li>
              <li class="team">
                <a href="brewers.html">Milwaukee Brewers</a>
              </li>
              <li class="team">
                <a href="pirates.html">Pittsburgh Pirates</a>
              </li>
              <li class="team">
                <a href="cardinals.html">St Louis Cardinals</a>
              </li>
            </ul>
          </li>
          <li class="division">
            <button class="list-toggle js-list-toggle">West</button>
            <ul class="team-list" aria-expanded="false">
              <li class="team">
                <a href="diamondbacks.html">Arizona Diamondbacks</a>
              </li>
              <li class="team">
                <a href="rockies.html">Colorado Rockies</a>
              </li>
              <li class="team">
                <a href="dodgers.html">Los Angeles Dodgers</a>
              </li>
              <li class="team">
                <a href="padres.html">San Diego Padres</a>
              </li>
              <li class="team">
                <a href="giants.html">San Francisco Giants</a>
              </li>
            </ul>
          </li>
        </ul>
      </li>
    </ul>
  </nav>

</body>

              
            
!

CSS

              
                // Variables

$text-color: #444;
$border-color: rgba(black, 0.1);

// Mixins

@mixin accordion(
  // Defaults
  $duration: 0.5s,
  $easing: ease
  ) {
  position: relative; // ...so we can absolutely position the pseudoelement
  &:after {
    content: '\25bc'; // ‘Black Down-Pointing Triangle’
    position: absolute;
    right: 0.5em;
    transition: transform $duration $easing;
  }
  & + ul {
    max-height: 0;
    overflow: hidden;
    transition: max-height $duration $easing;
  }
  &.list-open {
    &:after {
      transform: rotateX(180deg);
    }
    & + ul {
      max-height: 100vh;
    }
  }
}

// SCSS

// Quickie global reset
* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  color: $text-color;
  font-family: 'Helvetica', 'Arial', sans-serif;
}

ul {
  list-style: none;
  width: 15em;
}

button,
a {
  display: block;
  padding: 0.5em;
  border-bottom: 1px solid $border-color;
}

// Make a button look like a link
button {
  background: none;
  border: 0;
  border-bottom: 1px solid $border-color;
  color: $text-color;
  font-family: inherit;
  font-size: 1em;
  text-align: left;
  width: 100%;
  &:hover {
    cursor: pointer;
  }
}

a {
  color: $text-color;
  text-decoration: none;
}

.list-toggle {
  @include accordion;
}

.main-navigation {
  margin: 2em;
}

.league-list {
  background-color: #ccc;
}

.division-list {
  background-color: #ddd;
}

.team-list {
  background-color: #eee;
}

              
            
!

JS

              
                $(function() {

  $('.js-list-toggle').click(function() {
    if ($(this).hasClass('list-open')) {
      $(this).removeClass('list-open')
        .next().attr('aria-expanded', 'false');
    } else {
      $(this).addClass('list-open')
        .next().attr('aria-expanded', 'true');
    }
  });

});

              
            
!
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