.header{
    display: flex;
    justify-content: space-between;
    padding: 10px;
    background-color: gray;
}

h1 > a{
    font-family: 'Times New Roman', Times, serif;
    color: white;
    text-decoration: none;
}

.menu{
    text-decoration: none;
    font-size: 25px;
    margin-bottom: 20px;
}

.dropdown_menu a{
    display: block;
    color: white;
    text-decoration: none;
}

.dropdown_menu > li,
.dropdown_menu > li li{
    position: relative;
    display: inline-block;
    width: 200px;
    padding: 6px 15px;
    background-color: gray;

}

.dropdown_menu > li li:hover {
    background:#737373; 
}

.dropdown_menu ul {
    position: absolute;
    top: 2em; left: 0;
    max-height:0em;	
    margin: 0; padding: 0;
    background-color: #ddd;
    overflow: hidden;
    transition: 0.5s max-height 0.1s;
    border-radius: 0 0 8px 8px;
}

.dropdown_menu > li:hover ul {
    max-height: 400px;
}