Помогите создать трёхуровневое меню на css [требует правки]

*{ 
  margin:0; 
  padding:0; 
  box-sizing:border-box; 
} 
.main-menu{ 
  width:500px; 
  height:50px; 
  background-color:#444; 
  display:flex; 
  list-style:none; 
  font-family:arial; 
  color:#eee; 
  justify-content: space-around; 
  margin: auto; 
} 
.main-menu > .main-list{ 
  line-height:50px; 
  width:100%; 
  text-align:center; 
  cursor:pointer; 
} 
.main-menu > .main-list:hover{ 
  background-color:#eee; 
  color:#555; 
} 
.main-menu > .main-list > .second-menu{ 
  display:none; 
  list-style:none; 
} 
.main-menu > .main-list:hover > .second-menu{ 
  display:block; 
} 
.main-menu > .main-list > .second-menu > .second-list:hover{ 
  background-color:#ddd; 
} 
.main-menu > .main-list > .second-menu > .second-list{ 
  height:50px; 
  background-color:#eee; 
} 
.main-menu > .main-list > .second-menu > .second-list > .third-menu{ 
  display:none; 
  margin-left:100%; 
  margin-top:-50px; 
  list-style:none; 
  color:#eee; 
} 
.main-menu > .main-list > .second-menu > .second-list > .third-menu > .third-list{ 
  text-align:center; 
  width: 150px; 
  background-color:#777; 
} 
.main-menu > .main-list > .second-menu > .second-list > .third-menu > .third-list:hover{ 
  background-color:#566 
} 
.main-menu > .main-list > .second-menu > .second-list:hover > .third-menu{ 
  display:block; 
}

<ul class="main-menu"> 
    <li class="main-list">Menu 1 
      <ul class="second-menu"> 
        <li class="second-list">Second 
          <ul class="third-menu"> 
            <li class="third-list">Third</li> 
          </ul> 
        </li> 
        <li class="second-list">Second 
          <ul class="third-menu"> 
            <li class="third-list">Third</li> 
            <li class="third-list">Third</li> 
            <li class="third-list">Third</li> 
            <li class="third-list">Third</li> 
          </ul> 
        </li> 
      </ul> 
    </li> 
    <li class="main-list">Menu 2 
      <ul class="second-menu"> 
        <li class="second-list">Second 
          <ul class="third-menu"> 
            <li class="third-list">Third</li> 
          </ul> 
        </li> 
        <li class="second-list">Second 
          <ul class="third-menu"> 
            <li class="third-list">Third</li> 
            <li class="third-list">Third</li> 
            <li class="third-list">Third</li> 
            <li class="third-list">Third</li> 
          </ul> 
        </li> 
      </ul> 
    </li> 
    <li class="main-list">Menu 3</li> 
  </ul>