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HTML

              
                <div class="accordion"> 
  
  <a href="#" class="accordion-toggle">Hover for height animate</a>
  <div class="accordion-content">
    <div class="accordion-inner"> 
      <p>For animate the "height" of element with CSS Transitions you need use "max-height".</p>
      <p>If use the "height: auto", the effect not works. Is necessary some value for the CSS create a CSS animate, and you can use "max-height" with a great value for emulate this effect.</p> 
    </div>
  </div>
</div>
              
            
!

CSS

              
                body{
  font-family: helvetica;
  font-size: 18px;
  text-align: center;
}

.accordion{ 
  display: inline-block;
  text-align: left;
  margin: 1%;
  width: 70%; 
  
  &:hover{
  
    // max-height technique
    .accordion-content{
      // If use the "height: auto", the effect not works. Is necessary some value for the CSS create a CSS animate, and we can use "max-height" with a great value for emulate this effect.
      max-height: 300px;
    }
  
  }
}

.accordion-content{
  -webkit-transition: max-height 1s; 
  -moz-transition: max-height 1s; 
  -ms-transition: max-height 1s; 
  -o-transition: max-height 1s; 
  transition: max-height 1s;  
  background: #e5feff;
  overflow: hidden;
  // "height: 0" not work with css transitions
  max-height: 0;
}

.accordion-inner{
  padding: 0 15px;
}

.accordion-toggle{
  -webkit-transition: background .1s linear;   
  -moz-transition: background .1s linear;   
  -ms-transition: background .1s linear;   
  -o-transition: background .1s linear;   
  transition: background .1s linear;   
  background: #00b8c9;
  border-radius: 3px;
  color: #fff;
  display: block;
  font-size: 30px;
  margin: 0 0 10px;
  padding: 10px;
  text-align: center;
  text-decoration: none;
  
  &:hover{
    background: darken(#00b8c9, 15%);
  }
  
}


              
            
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JS

              
                
              
            
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999px

Console