#nav_menu ul li a {
text-align: center;
display: block;
width: 175px;
padding: 1em 0;
text-decoration: none;
background-color: blue;
color: white;
font-weight: bold;
border-right: 2px solid white;
}

#nav_menu ul {
list-style-type: none;
position: relative;
}
#nav_menu ul li {
float: left;
}
#nav_menu ul ul {
display: none;
position: absolute;
top: 100%;
}

#nav_menu ul ul li { 
float: none;}
#nav_menu ul li:hover > ul {
display: block; }
#nav_menu > ul::after {
content: "";
display: block;
clear: both; }