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CSS

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HTML 

              
                .accordion
  h1.accordion__title ACCORDION
  .accordion__item
    .accordion__header
      h2.accordion__header-title Title 01
      i.accordion__header-toggle
    .accordion__content
      h3.accordion__content-title Lorem ipsum dolor sit amet, consectetur adipisicing elit.
      p.accordion__content-text
        | Lorem ipsum dolor sit amet, consectetur adipisicing elit. Quas, repellat vel et neque at asperiores recusandae necessitatibus voluptatum magnam. Odio est, repellendus quas molestias laborum itaque perspiciatis perferendis consequuntur quidem. Non ullam velit eaque accusantium nam, voluptates earum ab, placeat quaerat commodi delectus vel, magni maxime itaque dicta consequatur quisquam maiores nisi.

  .accordion__item
    .accordion__header
      h2.accordion__header-title Title 02
      i.accordion__header-toggle
    .accordion__content
      h3.accordion__content-title Lorem ipsum dolor sit amet, consectetur adipisicing elit.
      p.accordion__content-text
        | Lorem ipsum dolor sit amet, consectetur adipisicing elit. Quas, repellat vel et neque at asperiores recusandae necessitatibus voluptatum magnam. Odio est, repellendus quas molestias laborum itaque perspiciatis perferendis consequuntur quidem. Non ullam velit eaque accusantium nam, voluptates earum ab, placeat quaerat commodi delectus vel, magni maxime itaque dicta consequatur quisquam maiores nisi.

  .accordion__item
    .accordion__header
      h2.accordion__header-title Title 03
      i.accordion__header-toggle
    .accordion__content
      h3.accordion__content-title Lorem ipsum dolor sit amet, consectetur adipisicing elit.
      p.accordion__content-text
        | Lorem ipsum dolor sit amet, consectetur adipisicing elit. In autem sapiente maxime dignissimos voluptatum maiores, id quae temporibus cumque amet omnis, quidem distinctio, consequatur nostrum explicabo corrupti sit. Corrupti, qui?  Lorem ipsum dolor sit amet, consectetur adipisicing elit. Doloribus perspiciatis, nemo soluta voluptas quisquam, fugiat. Assumenda similique nam, totam voluptate, sed perferendis vero ea a cumque magnam quas. Illum, facere.

  .accordion__item
    .accordion__header
      h2.accordion__header-title Title 04
      i.accordion__header-toggle
    .accordion__content
      h3.accordion__content-title Lorem ipsum dolor sit amet, consectetur adipisicing elit.
      p.accordion__content-text
        | Lorem ipsum dolor sit amet, consectetur adipisicing elit. Reprehenderit nam obcaecati deleniti suscipit libero mollitia ullam eaque debitis velit ipsam molestias atque maiores placeat perspiciatis quo earum fugit incidunt, quaerat.  Lorem ipsum dolor sit amet, consectetur adipisicing elit. Suscipit repudiandae cumque placeat nemo asperiores vitae et saepe veritatis! Ea neque quas assumenda laudantium dolorem suscipit repellendus obcaecati, rem odit nihil.

  .accordion__item
    .accordion__header
      h2.accordion__header-title Title 05
      i.accordion__header-toggle
    .accordion__content
      h3.accordion__content-title Lorem ipsum dolor sit amet, consectetur adipisicing elit.
      p.accordion__content-text
        | Lorem ipsum dolor sit amet, consectetur adipisicing elit. Vitae dolorum veritatis voluptatibus provident a nihil doloribus nisi quas, exercitationem dicta rem incidunt repudiandae dolorem quam. Fuga omnis, ea quaerat. Odit. Lorem ipsum dolor sit amet, consectetur adipisicing elit. Possimus nesciunt ad quod quo, debitis deleniti cumque. Autem unde, aperiam nisi odit nihil quos nostrum eaque? Necessitatibus saepe neque delectus delenit.
!

CSS 

              
                $base-color: #18202a;

* {
  box-sizing: border-box;
}

body {
  min-height: 100vh;
  font-size: 1rem;
  line-height: 1.7;
  background-color: #337a95;
  padding: 20px;
  display: flex;
  justify-content: center;
  align-items: center;
}

.accordion {
  max-width: 600px;
  margin: auto;
  background-color: $base-color;
  box-shadow: 3px 3px 5px rgba(0,0,0,0.75);
 
  &__title {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100px;
    color: #fff;
    font-size: 1.3rem;
    font-weight: bold;
    background-color: lighten($base-color, 7%);
    border-bottom: 3px solid darken($base-color, 5%);
    letter-spacing: 0.25rem;
  }
  
  &__item {
    background-color: $base-color;
    
    &:nth-of-type(even) {
      background-color: darken($base-color, 5%);
    }
  }
  
  &__header {
    display: flex;
    align-items: center;
    position: relative;
    padding: 20px;
    cursor: pointer;
    border-bottom: 2px solid darken($base-color, 5%);
    transition: all 0.2s ease;
  
    &-title {
      color: #fff;
      font-weight: bold;
    }
    
    &-toggle {
      transition: transform 0.25s ease 0.1s;
      position: absolute;
      right: 20px;
      width: 10px;
      height: 10px;
      transform: rotate(-45deg);
      border-right: 2px solid #fff;
      border-bottom: 2px solid #fff;
    }

    &:hover {
      background-color: #000;
    }

    &--active {
      background-color: #000;
      
      .accordion__header-toggle {
        transform: rotate(45deg);
      }
    }
  }
  
  &__content {
    transition: 
      opacity 1s ease 0.25s, 
      height 0.25s ease;
    background-image: 
      linear-gradient(135deg, rgba(0,0,0,0.6) 0%, rgba(0,0,0,0.8) 75%),
      url(http://lorempixel.com/480/480/);
    background-size: cover;
    background-color: $base-color;
    padding: 0 5%;
    height: 0;
    overflow: hidden;
    opacity: 0;
    overflow-y: scroll;
    -ms-overflow-style: none;
    scrollbar-width: none;
    
    &::-webkit-scrollbar {
      display:none;
    }

    &-title {
      transition: 
        opacity 0.3s ease 0.3s, 
        transform 0.3s ease 0.3s;
      transform: scaleY(0);
      color: #ffe;
      opacity: 0;
      margin: 20px 0;
      font-size: 1.3rem;
      font-weight: bold;
      text-shadow: 0 1px 1px rgba(255,255,255,0.1);
    }

    &-text {
      transition: 
        opacity 0.3s ease 0.6s,
        transform 0.3s ease 0.6s;
      transform: scaleY(0);
      margin-bottom: 30px;
      color: rgba(255,255,255,0.65);
      opacity: 0;
    }

    &--show {
      height: 400px;
      opacity: 1;

      .accordion__content-title {
        opacity: 1;
        transform: scaleY(1);
      }

      .accordion__content-text {
        opacity: 1;
        transform: scaleY(1);
      }
    }
  }
}
!

JS 

              
                const accordionHeaders = document.querySelectorAll('.accordion__header');

function accordion(target) {
  target.classList.toggle('accordion__header--active');
  target.nextElementSibling.classList.toggle('accordion__content--show');
}

for(let $i = 0; $i < accordionHeaders.length; $i++) {
  let accordionHeader = accordionHeaders[$i];
  accordionHeader.addEventListener('click', () => {
    accordion(accordionHeader);
  });
}
!
999px

Console