How To Chnage The Design of Divi Default Menu

Apply This CSS code:

#top-menu li li a {
border: 1px solid whitesmoke;
margin-bottom: 15px;
text-align: center;
}

#top-menu li li a:hover {
color: #ffde00;
background: black;
opacity: 1!important;
}

.nav li ul {
border-top: 0px solid #0dbad8;
margin-top: -10px;

}

.nav li ul {
width: 380px;
}

#top-menu li li a {
width: 350px;
}