<div class="container">
  <div class="folder">
   <div class="paper">
      <h1>Sample paper</h1>
      <p>Lorem ipsum dolor sit amets, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet. Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.</p>
      <p>Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet. Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.</p>
      <p>Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet. Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.</p>
    </div>
    <div class="cover">
      <div class="title">Don't open</div>
    </div>
  </div>
</div>

@import "compass/css3";

$color-folder: #fab62f;

// Inverts a location so that top gets bottom and left gets right etc.
@function invert-location($location) {
  @if $location == left {
    @return right;  
  }
  @elseif $location == right {
    @return left;  
  }
  @elseif $location == top {
    @return bottom;  
  }
  @elseif $location == bottom {
    @return top;  
  }
}

// Gets the start position left on horizontal and top on vertical
@function position-start($location) {
  @if $location == top or $location == bottom {
    @return left;
  }
  @else {
    @return top;
  }
}

// Gets the end position right on horizontal and bottom on vertical
@function position-end($location) {
  @if $location == top or $location == bottom {
    @return right;
  }
  @else {
    @return bottom;
  }
}

// Decides if size needs to be height or width based on horizontal or vertical 
@function size-property($location) {
  @if $location == top or $location == bottom {
    @return width;
  }
  @else {
    @return height;
  }
}

/* 
   Generates the negative triangle as part of a offset with :before and :after

   $location: Where you want the negative triangle [top, right, bottom, left]

   $position: In percentage where the negative triangle should be placed. With 50% the cut out triangle is in the center.

   $size: How much will the surface be extruded in order to cut out the triangle. Can be any valid size (px, em, rem, % etc.)

   $color: The color of the extruded part where the triangle gets cut out
*/
@mixin negative-css-triangle($location: top, $position: 50%, $size: 30px, $color: black) {
  &:before, &:after {
    box-sizing: border-box;
    content: "";
    display: block;
    position: absolute;
    #{$location}: -$size * 2;
    border: $size solid transparent;
  }
  
  &:before {
    #{position-start($location)}: 0;
    #{size-property($location)}: $position;
    border-#{position-start($location)}: none;   
    border-#{invert-location($location)}-color: $color;
  }
      
  &:after {
    #{position-end($location)}: 0;
    #{size-property($location)}: 100% - $position;
    border-#{position-end($location)}: none;
    border-#{invert-location($location)}-color: $color;
  }  
}

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

html, body {
  height: 100%;
  width: 100%;
  background-color: shade($color-folder, 60%);
}

.container {
  position: relative;
  width: 100%;
  height: 100%;
        
  > .folder {
    width: 220px;
    height: 180px;
    left: calc(50% - 110px);
    top: calc(70% - 90px);
    position: absolute;
    
    > .cover {
      cursor: pointer;
      position: absolute;
      width: 100%;
      height: 100%;
      background-color: $color-folder; 
      
      @include border-radius(0 0 10px 10px);
      @include box-shadow(5px 5px rgba(0, 0, 0, 0.2));
      
      @include negative-css-triangle(top, 50%, 50px, $color-folder);
      
      > .title {
        position: absolute;
        padding: 1em;
        font-family: Arial, Helvetica, sans-serif;
        text-transform: uppercase;
        font-weight: bold;
        text-align: center;
        font-size: 2.5em;
        color: rgba(0, 0, 0, 0.1);
        @include user-select(none);
        
        @include transform(rotate(20deg));
      }
    }
    
    > .paper {
      opacity: 1;
      position: absolute;
      overflow: hidden;
      width: 200px;
      height: 200px;      
      top: calc(50% - 150px);
      left: calc(50% - 100px);
      
      transition: top 0.5s, opacity 0.4s;
      
      font-family: Verdana, Tahoma, sans-serif;
      font-size: 0.1em;
      padding: 1em;
      color: shade($color-folder, 60%);
      background-color: tint($color-folder, 60%);
      
      @include box-shadow(10px 10px rgba(0, 0, 0, 0.2));
      @include border-radius(5px);
    }
    
    &:hover {
      > .paper {
        top: calc(50% - 200px);
      }
    }
    
    &.opened {
      > .paper {
        top: calc(-500px);
        opacity: 0;
      }
    }
  }
  
}

$(document).on('click', '.folder', function() {
  $(this).toggleClass('opened');
});