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CSS

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JavaScript

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HTML 

              
                <h1>Checkbox-Hack Accordion</h1>

<div class="accordion">

  <input class="accordion__input" type="radio" id="batman" name="accordion" checked />
  <div class="accordion__item" id="batman-content">
    <h2>Batman</h2>
    <p>Batman is a fictional superhero appearing in American comic books published by DC Comics. The character was created by artist Bob Kane and writer Bill Finger, and first appeared in Detective Comics #27 in 1939. Originally named the "Bat-Man," the character is also referred to by such epithets as the Caped Crusader, the Dark Knight, and the World's Greatest Detective.</p>
  </div>
  <label for="batman" id="batman-button" class="accordion__button">Batman</label>

  <input class="accordion__input" type="radio" id="superman" name="accordion" />
  <div class="accordion__item" id="superman-content">
    <h2>Superman</h2>
    <p>Superman is a fictional superhero. The character was created by writer Jerry Siegel and artist Joe Shuster, and first appeared in Action Comics #1, a comic book published on April 18, 1938. The character regularly appears in comic books published by DC Comics, and has been adapted to a number of radio serials, movies, and television shows.</p>
  </div>
  <label for="superman" id="superman-button" class="accordion__button">Superman</label>


  <input class="accordion__input" type="radio" id="spiderman" name="accordion" />
  <div class="accordion__item" id="spiderman-content">
    <h2>Spiderman</h2>
    <p>Spider-Man is a fictional superhero created by writer-editor Stan Lee and writer-artist Steve Ditko. He first appeared in the anthology comic book Amazing Fantasy #15 (August 1962) in the Silver Age of Comic Books. He appears in American comic books published by Marvel Comics, as well as in a number of movies, television shows, and video game adaptations set in the Marvel Universe.</p>
  </div>
  <label for="spiderman" id="spiderman-button" class="accordion__button">Spiderman</label>

  
</div>
!

CSS 

              
                // Colors
$color1: #f0f0f0;
$color2: #f6f9fa;
$color3: #ffffff;
$color4: #22caeb;
$color5: #333333;


// General styles
body {
  padding: 10%;
  font-size: 16px;
  background: $color1;
  @media(max-width: 768px) {
    padding: 10% 2% 10% 2%;
  }
}

* {
  box-sizing: border-box;
}

h1 {
  text-align: center;
}

// Accordion
.accordion {
  font-size: 0; // Remove gap between inline-block elements
  box-shadow: 0 0 10px rgba(0,0,0,0.2);
  position: relative;

  &__input {
    display: none;
  }

  &__input:checked + &__item {
    height: auto;
    opacity: 1;
  }

  // Enables highlihting selected tab
  &__input#batman:checked ~ &__button#batman-button,
  &__input#superman:checked ~ &__button#superman-button,
  &__input#spiderman:checked ~ &__button#spiderman-button {
    background: $color3;
    border-top-color: lighten($color4, 25%);
    opacity: 1;
  }

  &__button {
    font-size: 16px; // Reset font-size
    background: $color2;
    width: 33.3333333%;
    display: inline-block;
    padding: 20px;
    color: $color5;
    text-decoration: none;
    text-align: center;
    border-top: 3px solid transparent;
    transition: all 150ms ease-in-out;
    border-top-color: lighten($color5, 30%);
    cursor: pointer;
    opacity: 0.6;
    &:hover {
      border-top-color: lighten($color4, 35%);
      opacity: 1;
    }
  }

  &__item {
    font-size: 16px; // Reset font-size
    line-height: 1.5;
    position: absolute;
    top: 60px;
    padding: 20px;
    width: 100%;
    height: 0;
    overflow: hidden;
    background: $color3;
    opacity: 0;
  }
}
!

JS
!
999px

Console