Some questions about drop-down navigation menu_html/css_WEB-ITnose

CSS3

background: #292929;
background: -moz-linear-gradient(top, black, #3c3c3c 1px, #292929 25px);
background: -webkit-gradient( linear, left top, left 25, from(black),
The first one is the background color. What are the functions of the following two? I’m confused here recently when learning the drop-down navigation menu! Discussion (Solution)
Background color gradient can create a three-dimensional effect

The second one is for Firefox browser, and the third one is for IE browser