.dropdown, .dropdown * {
 font-size: 12px;  /* font size */
 line-height: normal;
 margin: 0;
 padding: 0;
}
.dropdown {
 border: solid 0px #000;  /* set the border line of the main menu */
}
.dropdown, .dropdown ul, .dropdown li {
 width: 150px;  /* set the width of the menu */
}
.dropdown a {
 display: block;
 padding: 2px 0.5em;
}
.dropdown a, .dropdown a:link, .dropdown a:hover, .dropdown a:visited {
 color: #000;  /* the color of letter */
 text-decoration: none;
}
.dropdown a:hover {  /* when mouse over */
 color: #00f;  /* the color of letter */
 background: #888;  /* the color of background */
}
.dropdown li {
 position: relative;
 display: block;
 list-style: none;
 background: #bbb;  /* the color of main menu's background */
}
.dropdown li li {
 background: #ccc;  /* the color of sub menu's background */
}
.dropdown ul {
 visibility: hidden;
 position: absolute;
 left: 150px;  /* same widht to the main menu */
 top: 0px;  /* minus of the width of borderline */
 border: solid 0px #000;  /* set the border line of the sub menu */
}
.dropdown li:hover > ul {
 visibility: visible;
}