CSS3-only Accordions!

how I code them.

With this tutorial I will show you how I implemented the accordion on the landing page of my website. It is based on CSS3, requires no JavaScript and is fully responsive.

Update: Scroll down to the end of the post for the final SASS code!

There is one main advantage of the approach presented here over others I found on the internet: The slides truly overlap each other. This prevents ugly text reflow during the animation (as seen in this prominent example, this one or this one) and allows for multiple lines of text in the captions (as opposed to this example).

Furthermore the horizontal accordion presented here is fully responsive - no fixed width is required; it will always fill 100% of its parent container (other accordions, such as this one or this one are hard-coded to a fixed width).

At first we will set up the basic behavior, then we will add background images and as a last step we will add captions. All style code will be provided as SASS code.

The Basic Bahavior

Here is the most basic version of the accordion. It has three items, each has a specific background color. If you hover over one slide it will expand, shrinking the others.

<div class="accordion">
  <ul>
    <li style="background:#963C0C"></li>
    <li style="background:#086348"></li>
    <li style="background:#658D0B"></li>
  </ul>
</div>
.accordion {

  ////////////////////////////////////////////////////////////
  // the first part of the style code is independent from   //
  // the number of slides in the accordion                  //
  ////////////////////////////////////////////////////////////

  // the accordion shall always have a fixed aspect ration in
  // order to prevent distortion. Therefore we set the height
  // to zero and define a bottom padding in percent. This is
  // done down in the second half.
  height: 0;

  position: relative;
  overflow: hidden;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 1);

  ul {
    margin: 0;
    padding: 0;

    // remove white space between slides
    font-size: 0;

    li {
      height: 0;
      margin: 0;
      padding: 0;
      display: inline-block;
      position: relative;
      border-top: 1px solid #373737;
      box-shadow: 0 2px 10px rgba(0, 0, 0, 1);
      @include transition(all 400ms);
    }
  }

  ////////////////////////////////////////////////////////////
  // this second part of the code will be adjusted when we  //
  // want to have more than three items in our accordion    //
  ////////////////////////////////////////////////////////////

  // some fixed values; they can be adjusted to change the
  // appearance of the accordion
  $slides:                  3;
  $accordion_aspect_ratio:  2/1;
  $slide_aspect_ratio:      16/10;

  // these values are required multiple times, therefore I
  // store them in some variables here
  $slide_h: 100% / $accordion_aspect_ratio;
  $slide_w: $slide_h * $slide_aspect_ratio;

  // this sets the height of the accordion
  padding-bottom: $slide_h;

  ul li {
    // the actual width of the slides; the size they will
    // cover when they are expanded
    width: $slide_w;

    // the negative right margin makes the slides overlap
    margin-right: 100% / $slides - $slide_w;

    // this sets the height of each slide
    padding-bottom: $slide_h;
  }

  // when the mouse is over the accordion, shrink all slides
  // to do this, we have to increase the negative right
  // margin so that the slides overlap more
  ul:hover li {
    margin-right: (100% - $slide_w) / ($slides - 1) - $slide_w;
  }

  // except for the hovered slide, this one is expanded
  // a margin-right of zero means that the next slide will
  // not overlap this one at all
  ul:hover li:hover {
    margin-right: 0;
  }
}

As you can see, the behavior is configured with three variables. $slides adjusts the number of supported entries, $accordion_aspect_ratio sets the aspect ratio of the accordion (when the size of the website changes, so will the accordion) and $slide_aspect_ratio. The latter describes the aspect ratio of the expanded slide and should not be set to a greater value than the $accordion_aspect_ratio.

Variable Number of Slides

Our next goal is to support any number of items. This can be achieved by replacing the bottom half of the style code above with a for-loop.

<div class="accordion accordion-items-8">
  <ul>
    <li style="background:#AC367D"></li>
    <li style="background:#DA7844"></li>
    <li style="background:#2D9072"></li>
    <li style="background:#A1CC40"></li>
    <li style="background:#DA85B9"></li>
    <li style="background:#FFBE9C"></li>
    <li style="background:#78C4AD"></li>
    <li style="background:#D7F495"></li>
  </ul>
</div>
// replace the "second part" of the .accordion
// class above with the following code
@for $slides from 3 through 10 {

  &.accordion-items-#{$slides} {

    // decrease height for increasing number of items
    $accordion_aspect_ratio: 1.3 + $slides / 5;
    $slide_aspect_ratio: 16/10;

    $slide_h: 100% / $accordion_aspect_ratio;
    $slide_w: $slide_h * $slide_aspect_ratio;

    padding-bottom: $slide_h;

    ul li {
      width: $slide_w;
      margin-right: 100% / $slides - $slide_w;
      padding-bottom: $slide_h;
    }

    ul:hover li {
      margin-right: (100%-$slide_w) / ($slides - 1) - $slide_w;
    }

    ul:hover li:hover {
      margin-right: 0;
    }
  }
}

Background images

As a next step, we want to add pictures to our accordion. To achieve this, we set a background image for each slide and add a little bit of styling to the <li> element of our accordion.

<div class="accordion accordion-items-4">
  <ul>
  <li style="background-image:url('http://lorempixel.com/560/420/nature/1')"></li>
  <li style="background-image:url('http://lorempixel.com/560/420/nature/2')"></li>
  <li style="background-image:url('http://lorempixel.com/560/420/nature/3')"></li>
  <li style="background-image:url('http://lorempixel.com/560/420/nature/4')"></li>
  </ul>
</div>
// add this to the appropriate
// place in the accordion class
.accordion {
  ul li {
    background-repeat: no-repeat;
    background-position: center center;
    background-size: cover;
  }
}

Captions

Finally we want to have some captions on our slides. Since they should look really awesome we will add some transitions!

  • Lorem Ipsum

    Lorem ipsum dolor sit amet, consectetur adipisicing elit.
    read on »

  • Lorem Ipsum

    Lorem ipsum dolor sit amet, consectetur adipisicing elit.
    read on »

  • Lorem Ipsum

    Lorem ipsum dolor sit amet, consectetur adipisicing elit.
    read on »

  • Lorem Ipsum

    Lorem ipsum dolor sit amet, consectetur adipisicing elit.
    read on »

<div class="accordion accordion-items-4">
  <ul>
    <li style="background-image:url('http://lorempixel.com/560/420/nature/5')">
      <div>
        <h2>Lorem Ipsum</h2>
        <p>Lorem ipsum...
           <br><a href="#">read on »</a>
        </p>
      </div>
    </li>
    <li style="background-image:url('http://lorempixel.com/560/420/nature/6')">
      <div>
        <h2>Lorem Ipsum</h2>
        <p>Lorem ipsum...
           <br><a href="#">read on »</a>
        </p>
      </div>
    </li>
    <li style="background-image:url('http://lorempixel.com/560/420/nature/7')">
      <div>
        <h2>Lorem Ipsum</h2>
        <p>Lorem ipsum...
           <br><a href="#">read on »</a>
        </p>
      </div>
    </li>
    <li style="background-image:url('http://lorempixel.com/560/420/nature/8')">
      <div>
        <h2>Lorem Ipsum</h2>
        <p>Lorem ipsum ...
           <br><a href="#">read on »</a>
        </p>
      </div>
    </li>
  </ul>
</div>
// add this to the appropriate
// place in the accordion class
.accordion {
  ul li {
    font-size: 14px;

    div {
      position: absolute;
      bottom: 0;
      width: 100%;
      padding: 20px;

      overflow: hidden;
      opacity: 0;

      @include transition(all 300ms);
      @include background-image(linear-gradient(top, rgba(0,0,0,0) 0%,rgba(0,0,0,1) 100%));

      h2 {
        @include transition(all 500ms);
        @include translateX(-30px);
      }

      a {
        display: inline-block;
        @include transition(all 500ms);
        @include translateX(-30px);
      }

      p {
        display: inline-block;
        @include transition(all 500ms);
        @include translateX(-60px);
      }
    }

    &:hover div {
      opacity: 1;

      h2, a, p {
        @include translateX(0px);
      }
    }
  }
}

Final Words

That’s it! I hope you can use this technique somewhere. If you have further questions just use the comment form below! And it would be awesome if you could post a link if you used this accordion somewhere! Below you find the final SASS class.

.accordion {

  ////////////////////////////////////////////////////////////
  // the first part of the style code is independent from   //
  // the number of slides in the accordion                  //
  ////////////////////////////////////////////////////////////

  // the accordion shall always have a fixed aspect ration in
  // order to prevent distortion. Therefore we set the height
  // to zero and define a bottom padding in percent. This is
  // done down in the second half.
  height: 0;

  position: relative;
  overflow: hidden;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 1);

  ul {
    margin: 0;
    padding: 0;

    // remove white space between slides
    font-size: 0;

    li {
      height: 0;
      margin: 0;
      padding: 0;
      display: inline-block;
      position: relative;
      border-top: 1px solid #373737;
      box-shadow: 0 2px 10px rgba(0, 0, 0, 1);
      @include transition(all 400ms);

      // these three lines are only required if you
      // are using background images
      background-repeat: no-repeat;
      background-position: center center;
      background-size: cover;

      // from here to the and of li is only necessary
      // if you want to have captions
      font-size: 14px;

      div {
        position: absolute;
        bottom: 0;
        width: 100%;
        padding: 20px;

        overflow: hidden;
        opacity: 0;

        @include transition(all 300ms);
        @include background-image(linear-gradient(top, rgba(0,0,0,0) 0%,rgba(0,0,0,1) 100%));

        h2 {
          @include transition(all 500ms);
          @include translateX(-30px);
        }

        a {
          display: inline-block;
          @include transition(all 500ms);
          @include translateX(-30px);
        }

        p {
          display: inline-block;
          @include transition(all 500ms);
          @include translateX(-60px);
        }
      }

      &:hover div {
        opacity: 1;

        h2, a, p {
          @include translateX(0px);
        }
      }
    }
  }

  ////////////////////////////////////////////////////////////
  // this second part of the code provides sub classes for  //
  // different item counts                                  //
  ////////////////////////////////////////////////////////////

  @for $slides from 3 through 10 {

    &.accordion-items-#{$slides} {

      // decrease height for increasing number of items
      $accordion_aspect_ratio: 1.3 + $slides / 5;
      $slide_aspect_ratio: 16/10;

      $slide_h: 100% / $accordion_aspect_ratio;
      $slide_w: $slide_h * $slide_aspect_ratio;

      padding-bottom: $slide_h;

      ul li {
        width: $slide_w;
        margin-right: 100% / $slides - $slide_w;
        padding-bottom: $slide_h;
      }

      ul:hover li {
        margin-right: (100%-$slide_w) / ($slides - 1) - $slide_w;
      }

      ul:hover li:hover {
        margin-right: 0;
      }
    }
  }
}


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