<ul id="dropdown1">
   <li>
     <a href="#">AL East     </a>
     <ul>
       <li>
         <a href="#">Baltimore Orioles         </a>
       </li>
       <li>
         <a href="#">Boston Red Sox         </a>
       </li>
       <li>
         <a href="#">New York Yankees         </a>
       </li>
       <li>
         <a href="#">Tampa Bay Rays         </a>
       </li>
       <li>
         <a href="#">Toronto Blue Jays         </a>
       </li>     </ul>
   </li>
   <li>
     <a href="#">AL Central     </a>
     <ul>
       <li>
         <a href="#">Chicago White Sox         </a>
       </li>
       <li>
         <a href="#">Cleveland Indians         </a>
       </li>
       <li>
         <a href="#">Detroit Tigers         </a>
       </li>
       <li>
         <a href="#">Kansas City Royals         </a>
       </li>
       <li>
         <a href="#">Minnesota Twins         </a>
       </li>     </ul>
   </li>
   <li>
     <a href="#">AL West     </a>
     <ul>
       <li>
         <a href="#">Houston Astros         </a>
       </li>
       <li>
         <a href="#">Los Angeles Angels         </a>
       </li>
       <li>
         <a href="#">Oakland Athletics         </a>
       </li>
       <li>
         <a href="#">Seattle Mariners         </a>
       </li>
       <li>
         <a href="#">Texas Rangers         </a>
       </li>     </ul>
   </li> </ul>

In style element (<style>) within head element:

#dropdown1 {
  padding: 0;
  margin: 0;
  list-style: none;
  display: flex;
}
#dropdown1 li {
  flex-basis: 12em;
  flex-grow: 0;
  flex-shrink: 0;
  padding: 0;
  margin: 0;
  display: block;
}
#dropdown1 li ul {
  display: none;
  padding: 0;
  margin:0;
  }
#dropdown1 li:hover ul { display: block; }