Codeigniter nivoslider images and css background images not showing?
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I am writing a webpage with CI. I am a newbie. I cant manage to show my imagefiles on the page .
My directory structure is 

    +application
    +system
    +assets
      +css
      +js
      +images

I use nivoslider in a part and here is the div part : 

    <div id="slider-nivo">
    <img src="<?php echo base_url(); ?>assets/images/nivoslider1.jpg" alt="" />
    <img src="<?php echo base_url(); ?>assets/images/nivoslider2.jpg" alt="" />
    <img src="<?php echo base_url(); ?>assets/images/nivoslider3.jpg" alt="" />

and also in css there is a part texturing the menu , I cant make the background picture work:

     #sidebar #sidebar-content #menu  li {background-image: url('../images/menu_li.png');

How can I show the pictures in the view and the css backgrounds?