Full-Width Panel Expansion, CSS only

full-width-panel-expansion-css-only.markdown

Full-Width Panel Expansion, CSS only

A CSS only expanding panel gallery with keyboard support and CSS Vars to progressively enhance with animation.

The keyboard support is probably not truly accessible. I'll leave it as an exercise to the reader to add real accessibility aria-roles and JavaScript.

Thanks to @davidkpiano for help with setup and the Animation At Work community for helpful feedback.

Like sliding panels? Try these transform-based sliding panels

A Pen by Shaw on CodePen.

License.

index.html

<div class="panels">
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
</div>


<div class="panels">
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
</div>


<div class="panels">
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
</div>


<div class="panels">
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
</div>


<div class="panels">
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
</div>


<div class="panels">
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
  <a href="javascript:void(0)" class="panel">
    <div class="panel__content"></div>
  </a>
</div>

scripts

<script src="https://codepen.io/shshaw/pen/epmrgO"></script>

style.less

@images: 
  'https://unsplash.it/1000/1000/?image=760',
  'https://unsplash.it/1000/1000/?image=883',
  'https://unsplash.it/1000/1000/?image=786',
  'https://unsplash.it/1000/1000/?image=342',
  'https://unsplash.it/1000/1000/?image=550',
  'https://unsplash.it/1000/1000/?image=821',
  'https://unsplash.it/1000/1000/?image=777';



.panels {
  overflow: hidden;
  display: flex; 
  position: relative;
  z-index: 1; 
}

.panel { 
  flex: 1;
  cursor: pointer;
  background-position: center center;
  background-size: cover;
}

.panel__content {
  width: 100%;
  height: 102%;
  overflow: hidden;
  cursor: pointer;
  background: inherit;
}

.panel:before,
.panel__content:before {
  content: ' ';
  display: block;
  width: 100%;
  height: 100%;
}

.panel:before {
  background: rgba(255,255,255,0.3);
  position: relative;
  z-index: 99;
  opacity: 0;
  transition: opacity 0.3s linear;
}

/* The non-CSS Var hover state */
.panel:hover,
.panel:focus {
  &:before { opacity: 1; }

  .panel__content { 
    position: absolute; 
    top: -1%;
    left: 0;
    z-index: 98;
  }
}



/* If CSS Vars are supported... */
@supports ( (--panel-support: 0) ) {


  .panel {
    --i: 0;
    --percent: ~"calc( ((var(--i) - 1) / var(--items)) * 100 )";
  }
  
  /* 
  A simple LESS loop to set up the CSS vars.

  Output will be something like
  .panels--1 { --items: 1; }
  .panth:nth-child(1) { --i: 1; }
  .panels--2 { --items: 2; }
  .panth:nth-child(2) { --i: 2; }

  ..up to the total number provided.
  */
  .panel-maker( length(@images) );
  .panel-maker(@total, @i: @total) when (@i > 0) {
    .panel-maker(@total, ( @i - 1 ) );  
    
    .panel:nth-last-child(n+@{i}), .panel:nth-last-child(n+@{i}) ~ .panel { --items: @i; }
    .panel:nth-child( @{i} ) { --i: @i; }
  }

  .panel__content {
    position: absolute;
    top: -1%;
    left: 0%;
    z-index: auto;
    transform: translateX( ~"calc( var(--percent) * 1% )" );

    &:before {
      background: inherit;
      transform: translateX(-50%) translateX( ~"calc(100% / var(--items) * 0.5 )" );
    }
  }
  
  .panel__content,
  .panel__content:before { 
    transition: transform 0.4s cubic-bezier(.44,.0,.0,1);
  }

  /* When there's an active hover on the container. This will apply to all panels in the container, unless overridden */
  .panels:hover .panel__content { 
      z-index: auto; 
      transform: translateX(0%);
  }

  /* Panels after the hovered panel */
  .panel:hover ~ .panel .panel__content { transform: translateX( 100% ); }
  
  /* The active panel */
  .panel:hover,
  .panel:focus {
    .panel__content { transform: translateX(0%); }
    .panel__content:before { transform: translateX(0%) scale(1.2); }
  }
  
  .panel:focus {
    .panel__content,
    .panel__content:before { transition: none !important; }
  }

}



/* 
//////////////////////////////////////
STYLISTIC CHOICES
//////////////////////////////////// 
*/

.panels { 
  box-shadow: 0 0 10rem rgba(0, 0, 0, 0.6);
  height: 40vh;
  margin: 10vh auto;
  min-height: 300px;
  max-height: 700px;
}
body > .panels:first-child { margin: 15vh auto; height: 65vh; }

/* Set up the background images */
.image-loop(@total, @i: 1) when (@i <= @total) {
  .image-loop(@total, ( @i + 1 ) );
  .panel:nth-child( @{i} ) {
    background-image: ~"url(" extract(@images, @i) ~")";
  }
}
.image-loop(length(@images));

html { height: 100%; }
body { min-height: 100%; }
html, body { margin: 0; padding: 0; }
body { background: #2F3C4F; }

*, *:before, *:after {
  box-sizing: border-box;
}