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HTML

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HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

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Insecure Resource

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CSS

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CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

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JavaScript

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Babel includes JSX processing.

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HTML 

              
                  <ul class="tree">
    <li><container><icon/>Animals</container>
      <ul>
        <li><folder><icon/>Birds</folder></li>
        <li><container><icon/>Mammals</container>
          <ul>
            <li><folder class="selected"><icon/>Elephant</folder></li>
            <li><folder><icon/>Mouse</folder></li>
          </ul>
        </li>
        <li><folder><icon/>Reptiles</folder></li>
      </ul>
    </li>
    <li>Plants
      <ul>
        <li>Flowers
          <ul>
            <li>Rose</li>
            <li>Tulip
              <ul>
                <li>List item 1</li>
                <li>List item 2
                  <ul>
                    <li>List item 2.1</li>
                    <li>List item 2.2</li>
                    <li>List item 2.3</li>
                  </ul>
                </li>
                <li>List item 3</li>
                <li>List item 4</li>
                <li>List item 5
                  <ul>
                    <li>List item 5.1</li>
                    <li>List item 5.2
                      <ul>
                        <li>List item 5.2.1</li>
                        <li>List item 5.2.2</li>
                        <li>List item 5.2.3</li>
                        <li>List item 5.2.4</li>
                      </ul>
                    </li>
                  </ul>
                </li>
                <li>List item 6</li>
                <li>List item 7</li>
                <li>List item 8</li>
              </ul>
            </li>
          </ul>
        </li>
        <li>Trees</li>
      </ul>
    </li>
  </ul>
!

CSS 

              
                body {
  background:white;
  font:normal normal 13px/1.4 Segoe,"Segoe UI",Calibri,Helmet,FreeSans,Sans-Serif;
  padding:50px;
}


/**
 * Framework starts from here ...
 * ------------------------------
 */

.tree,
.tree ul {
  margin:0 0 0 1em; /* indentation */
  padding:0;
  list-style:none;
  color:#369;
  position:relative;
}

.tree ul {margin-left:.5em} /* (indentation/2) */

.tree:before,
.tree ul:before {
  content:"";
  display:block;
  width:0;
  position:absolute;
  top:0;
  bottom:0;
  left:4px;
  border-left:1px dashed;
}

ul.tree:before {
  border-left:none
}

.tree li {
  margin:0;
  padding:0 1.5em; /* indentation + .5em */
  line-height:2em; /* default list item's `line-height` */
  font-weight:bold;
  position:relative;
}

.tree container, .tree folder {
  display: block;
}

.tree container icon, .tree folder icon {
  background-repeat: no-repeat;
  background-position: 4px center;
  padding-left: 24px;
}

.tree container icon {
  background-image: url('data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABEAAAAQCAYAAADwMZRfAAAAAXNSR0IArs4c6QAAAAlwSFlzAAALEwAACxMBAJqcGAAAAnJpVFh0WE1MOmNvbS5hZG9iZS54bXAAAAAAADx4OnhtcG1ldGEgeG1sbnM6eD0iYWRvYmU6bnM6bWV0YS8iIHg6eG1wdGs9IlhNUCBDb3JlIDUuNC4wIj4KICAgPHJkZjpSREYgeG1sbnM6cmRmPSJodHRwOi8vd3d3LnczLm9yZy8xOTk5LzAyLzIyLXJkZi1zeW50YXgtbnMjIj4KICAgICAgPHJkZjpEZXNjcmlwdGlvbiByZGY6YWJvdXQ9IiIKICAgICAgICAgICAgeG1sbnM6dGlmZj0iaHR0cDovL25zLmFkb2JlLmNvbS90aWZmLzEuMC8iCiAgICAgICAgICAgIHhtbG5zOnhtcD0iaHR0cDovL25zLmFkb2JlLmNvbS94YXAvMS4wLyI+CiAgICAgICAgIDx0aWZmOllSZXNvbHV0aW9uPjcyPC90aWZmOllSZXNvbHV0aW9uPgogICAgICAgICA8dGlmZjpDb21wcmVzc2lvbj41PC90aWZmOkNvbXByZXNzaW9uPgogICAgICAgICA8dGlmZjpYUmVzb2x1dGlvbj43MjwvdGlmZjpYUmVzb2x1dGlvbj4KICAgICAgICAgPHhtcDpDcmVhdG9yVG9vbD5GbHlpbmcgTWVhdCBBY29ybiA1LjIuMTwveG1wOkNyZWF0b3JUb29sPgogICAgICAgICA8eG1wOk1vZGlmeURhdGU+MjAxNi0wMi0wMlQxMjo0ODo1ODwveG1wOk1vZGlmeURhdGU+CiAgICAgIDwvcmRmOkRlc2NyaXB0aW9uPgogICA8L3JkZjpSREY+CjwveDp4bXBtZXRhPgqitOMRAAABuklEQVQ4EZVSvy9sQRT+Znfseh4rfuUVSCQahSBeIZaORqURT6L1FyjlFSJER0In0RMajeqphEVHqxIhmydYrL137sydce5ds9lYWesk9557vvOdb+acexjebXrtMqHjv2I2VtEnvTPT/mDjcp7bpKypX4Vxxm3MTOyKvn/buJwPRQYXTzYn+yLj3W2JJkvO5OTP68XUEWAmU3+TNxb/zLM/G+n1gc7I1FBnork5EYeQgCOAuxcf++f/ce+wXWmiz8XFDOxqe6Zl4Xhl8EdyNuVww9h0f0dDQ2Mdh+cDngakAeKxKMZ6W3D7LCaUT0CReQo3eiP9dHa3vAWQSJCrpndNYaRFbHD00PPRrh9V6+Flbj4T6doLchx0iKcNXLpFpSYLXDcs4dAKgkCnkPhayg3a8yVcVOdFpBJwlEZOfV1sGQFfSUESmbyIki6JmIpE2LuKS3xFh1vjSnkQBH5nJkE7gYgr8kJcKxm280r7UZHRdcJ2aCbWuO/L0/SjM5z1dK0Fy/mgpWxOZLWvTl2vKrxK2Obo0vE/gPWWKy7OGWYuDuaSIxYLN4kmPUFA6VZZVqn/xr8sLf4UeQNldMTNDtyI9wAAAABJRU5ErkJggg==');
}

.tree folder icon {
  background-image: url('data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABEAAAAQCAYAAADwMZRfAAAAAXNSR0IArs4c6QAAAAlwSFlzAAALEwAACxMBAJqcGAAAAnJpVFh0WE1MOmNvbS5hZG9iZS54bXAAAAAAADx4OnhtcG1ldGEgeG1sbnM6eD0iYWRvYmU6bnM6bWV0YS8iIHg6eG1wdGs9IlhNUCBDb3JlIDUuNC4wIj4KICAgPHJkZjpSREYgeG1sbnM6cmRmPSJodHRwOi8vd3d3LnczLm9yZy8xOTk5LzAyLzIyLXJkZi1zeW50YXgtbnMjIj4KICAgICAgPHJkZjpEZXNjcmlwdGlvbiByZGY6YWJvdXQ9IiIKICAgICAgICAgICAgeG1sbnM6dGlmZj0iaHR0cDovL25zLmFkb2JlLmNvbS90aWZmLzEuMC8iCiAgICAgICAgICAgIHhtbG5zOnhtcD0iaHR0cDovL25zLmFkb2JlLmNvbS94YXAvMS4wLyI+CiAgICAgICAgIDx0aWZmOllSZXNvbHV0aW9uPjcyPC90aWZmOllSZXNvbHV0aW9uPgogICAgICAgICA8dGlmZjpDb21wcmVzc2lvbj41PC90aWZmOkNvbXByZXNzaW9uPgogICAgICAgICA8dGlmZjpYUmVzb2x1dGlvbj43MjwvdGlmZjpYUmVzb2x1dGlvbj4KICAgICAgICAgPHhtcDpDcmVhdG9yVG9vbD5GbHlpbmcgTWVhdCBBY29ybiA1LjIuMTwveG1wOkNyZWF0b3JUb29sPgogICAgICAgICA8eG1wOk1vZGlmeURhdGU+MjAxNi0wMi0wMlQxMjo0OTowOTwveG1wOk1vZGlmeURhdGU+CiAgICAgIDwvcmRmOkRlc2NyaXB0aW9uPgogICA8L3JkZjpSREY+CjwveDp4bXBtZXRhPgrkd8ulAAACb0lEQVQ4EZVSTWgTQRT+ZjP5L21KIeAfFpTWikJVqJdeiuJF0qulePHqRcGriAdPXqrFQy8i6EHwIGigFEQQvbRQxP5pSkzbxCbpT9o0SZvs7uzu+HabTeslxQcz7++bb957Mwx1mRy92sp1w+f6lV3TGHj8Y8f1m2neSOoYE5LfcP1AmE+RfdP1j9Tx+12v/0y+3S5nZ6S78t8/lOL3ut4feZgAbOLR5RedvVeGT1y63s5DHTB0AcswsbuZw+r0xF4xt/KO+xSpKIBpWHREgcLx5drD6TfuBXY7t6PdvW3BFg5DFKFYBmAJhMIMnX0D4Ug+c0fxMDACWpZEMZtCKZ/WyT0gkcIE97bBwyPw+OojsonqEj1z3jUdvfhtHIXM8j8xbmgqLL0CqYcaCbslrbq370tJTdt17EutXIIQViT+4OI5QAOCIZPDH4SubUGtErgu+eRvzH76TC1IeIQK0xsg64CIKWxIcgwxoUCaKHNoNUDaAwOEJpBbmEO1WET/8C0nxqgSeagSJ0ibTWnjZuIfwUHD8pp0m6oiO78AWavgVPdZ+AMBBLmFXV1Bi8863JHDU9ooIDs3m4Yp7zqTrFZqKGfmiXoHHcePIdzeBiYq0C0//EYNOoIIQIWAlx6YiDfXsbq4kiisLD2NjSbHHZJcKk1pDSdPR9EajcCkyrx0VKNHCqKKqkG9E4kkgp3CFtZTqUQmsTwWG0m+sssiEjm19nOuv6fvQoh5FFQ21pxy3U11jG2i2Jf1pdX08q+ll4PPks9djDNy+vZfKdDjBptqxp7ERhYbBDbWaceAPsgbP60pBTqsvfoHao777+xfmRQTxswccNgAAAAASUVORK5CYII=');
}

.tree folder.selected {
  background-image: linear-gradient(to bottom, #e4eef5, #c0d1db);
  border-radius: 5px;
}

.tree folder:hover {
    background-image: linear-gradient(to bottom, #e9f5e7, #c3d9bf);
  border-radius: 5px;
}

.tree li:before {
  content:"";
  display:block;
  width:10px; /* same with indentation */
  height:0;
  border-top:1px dashed;
  margin-top:-1px; /* border top width */
  position:absolute;
  top:1em; /* (line-height/2) */
  left:4px;
}

ul.tree>li:before {
  border-top:none;
}

.tree li:last-child:before {
  background:white; /* same with body background */
  height:auto;
  top:1em; /* (line-height/2) */
  bottom:0;
}
!

JS
!
999px

Console