Change icon folder open and close in tree on ZK 7.0.2

See here zkfiddle:

<zk>
 <style>
   .z-tree-icon .z-tree-open {
     background-image: url(data:image/png;base64,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);
   /*background-image: url('https://az545221.vo.msecnd.net/skype-faq-media/faq_content/skype/screenshots/fa12330/emoticons/yawning_20.png');*/
     background-size: cover;
     width: 100%;
   }
   .z-tree-icon .z-tree-close {
     background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABQAAAAUCAYAAACNiR0NAAAAGXRFWHRTb2Z0d2FyZQBBZG9iZSBJbWFnZVJlYWR5ccllPAAAAxBJREFUeNqcVc9PE0EU/mZ3S1OogUILxEgsiAonGr2IBwMcjCdP3jxr1MRADybeOEkwHgoxUYP/hQfDCYgH8aKBE2iAQvjZUqCRQi3t7PjtTuVn0xgmeTv75r33zZt935sVKDHUZEOYUy+lixI5ZZ6iTFCGRWdi8XSsOAP2tSEGq6oPdT1AsBvwNZ90yMaB1DiwNQYU9obE7US0JKD9JVRDbVwEbkbQ/BSwGoo7ZJ3Hkbvw6ddCAoi/h9r5PkVzt3FnM30IaI8FXTCEbkVEy2OueomRQdkh/PTJQS2MAJvfNGhPKm25SdiqXwTaI6LpLndew/+NTY3LGJVLR9TOTD/VqJCjtWFY3rjR8YipLvOorId9ACyOArvLOtZ/Sc+ZFT1faALC9wCjggmwLkYT7OmPfM81G0ravahpBQ5mgRyN+XVg6TMQegh0J7TUPdDyT3dsjo/j68Q4scRwsCwUVJeormf1ZotHYcDBNtTlKGoDAXdle2fHnY/rYm2YMTyB3OLKFkT1VahV1WUpqSKCmWMvxYfkB/XwCBJZ+6i2zjtwUq+kDwobzJIJwISoIiCxLEi6SRplXnvLVdolxMprzCd1ZmJpwJ0Pddpg5oA/qw5HtLgYCpYqENCWekEjsjDkc2IAvvVXRYpouvqSg1o3qHusYzFwMRwsZmhDZ2nwTIUjB4O6UYY10j7GSauIYcMg6pTa/c3FgHY6jzDWwXCwSBs1IRMksxk6PyBjHQwHS/wZ8YZhmHHvjU7SZaFYNeD+E4G1ZOnTXiTLPn0o1tzDnq9oQe7HpPMdm92vnX3niZm1wT7P9XZ2wzQ5wT6tbyvfeUnydp/97u9A/ucM5HZqyPcsH9WAb60akmzcrG+MeFrZNdl5ZpsoD1jBzHxXkJ+bg0xuTPFy6fY9L6QPr6/9mKlB64IRz7U22rl7jsQ9IOFVkR7CJFAQ8DbS1Y/8r1k2SsoFq4zKdMkLdv+NiMG0+syGRl6JjTD8/hN2O5PhVbjBInAzWRiqfKGiZW9sZ+wNIswUyv8CBIarXuLML+CvAAMASDyP6pmxxvMAAAAASUVORK5CYII=);
   /*background-image: url('https://az545221.vo.msecnd.net/skype-faq-media/faq_content/skype/screenshots/fa12330/emoticons/speechless_20.png');*/
     background-size: cover;
     width: 100%;
   }
   /*remove the font awesome icon*/
   .z-tree-icon .z-tree-open::before,
   .z-tree-icon .z-tree-close::before {
     content: '';
   }
  </style>
<tree id="tree" width="400px" rows="8">
<treecols sizable="true">
<treecol label="Name" />
<treecol label="Description" />
</treecols>
<treechildren>
<treeitem>
<treerow>
<treecell label="Item 1" />
<treecell label="Item 1 description" />
</treerow>
</treeitem>
<treeitem>
<treerow>
<treecell label="Item 2" />
<treecell label="Item 2 description" />
</treerow>
<treechildren>
<treeitem>
<treerow>
<treecell label="Item 2.1" />
</treerow>
<treechildren>
<treeitem>
<treerow>
<treecell label="Item 2.1.1" />
</treerow>
</treeitem>
<treeitem>
<treerow>
<treecell label="Item 2.1.2" />
</treerow>
</treeitem>
</treechildren>
</treeitem>
<treeitem>
<treerow>
<treecell label="Item 2.2" />
</treerow>
<treechildren>
<treeitem>
<treerow>
<treecell label="Item 2.2.1" />
</treerow>
</treeitem>
</treechildren>
</treeitem>
</treechildren>
</treeitem>
<treeitem label="Item 3" />
</treechildren>
</tree></zk>