https://cssgradient.io/gradient-backgrounds/
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5 Pure CSS Treeview Menu Examples - DesignersLib.com
CSS Treeview Menu Demo / More Info Pure CSS Collapsible Tree Menu Demo More Info / Download Minimal CSS Tree Menu Demo / More Info Pure CSS Tree Menu Demo / More Info Pure CSS Tree Demo / More Info
http://www.designerslib.com/pure-css-treeview-menu/