Box-styled navigation menu

Here are the basics of making a horizontal navigation menu. It is one of my favorite things to do with CSS because you can really make some really nice looking menus with this. This is a simple code that can be used to start with:

ul {
    list-style-type: none;  /* This removes listing bullets */
    margin: 0;  /* Space outside this selector's content */
    padding: 0; /* Space between border and inside contents */
    overflow: hidden; /* I'm still trying to understand what it means */
    }
      
li {
    float: left; /* Will make listing horizontal. Starting from the left side.
                    Remove this if you want it to be the default vertical list */
    }
      
li a {
     display: block;  /* Displays a block-styled list */
     text-align: center;  /* All text will be centered */
     padding: 15px;
     text-decoration: none;  /* Remove default hyperlink decorations (underline) */
     background-color: #ddd;
    }

Displays: