added 'ubuntu-li.png' in static img and replaced in main.scss

assets/scss/libs/main.scss

@@ -188,7 +188,7 @@ ul.item-list li {
     margin: 0 0 0.25em 1.5em;
     padding: 0 0 0 20px;
     list-style-type: none;
-    background: url('https://www.ubuntu-it.org/sites/all/themes/light-drupal-theme/images/ubuntu-li.png') no-repeat left 4px;
+    background: url('../../images/pictograms/ubuntu-li.png') no-repeat left 4px;
     font-size: 14px;
     line-height: 20px;
 }
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