CSS : Is there a way to activate a hover element whitout activating the one below?

I know my question is hard to understand but I have made a gif to explain my problem. I would like the menu to go above the horizontal bar without activating it.
CSS of the vertical menu :

.dropbtn {
    color: white;
    padding: 5px 10px;
    border: none;
    cursor: pointer;
}

.dropbtn a {
    font-weight: bold;
    text-decoration: none;
    color: #ffffff;
}

.dropdown {
    position: relative;
    display: inline-block;
}

.dropdown-content {
    display: none;
    position: absolute;
    right: 0;
    text-align: left;
    background-color: #f9f9f9;
    min-width: 200px;
    z-index: 3;
    padding: 5px;
}

.dropdown-content a {
    color: black;
    padding: 12px 16px;
    text-decoration: none;
    display: block;
    z-index: 4;
}

.dropdown-content a:hover {
    background-color: #dddddd;
}

.dropdown:hover .dropdown-content {
    display: block;
    box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
}

.dropdown:hover .dropbtn {
    background-color: #ffffff;
    box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
}

.dropdown:hover .dropbtn a {
    color: #333333;
}

CSS of the horizontal bar :

nav {
    margin: 27px auto 0;

    position: relative;
    width: 800px;
    height: 50px;
    background-color: #34495e;
    border-radius: 8px;
    font-size: 0;
}

nav a {
    line-height: 50px;
    height: 100%;
    font-size: 15px;
    display: inline-block;
    position: relative;
    z-index: 1;
    text-decoration: none;
    text-transform: uppercase;
    text-align: center;
    color: white;
    cursor: pointer;
}

nav .animation {
    position: absolute;
    height: 100%;
    top: 0;
    z-index: 0;
    transition: all .5s ease 0s;
    border-radius: 8px;
}

a:nth-child(1) {
    width: 400px;
    z-index: 2;
}

a:nth-child(2) {
    width: 400px;
    z-index: 2;
}

nav .start-home,
a:nth-child(1):hover~.animation {
    width: 400px;
    left: 0;
    background-color: #39aeb4;
}

nav .start-likes,
a:nth-child(2):hover~.animation {
    width: 400px;
    left: 400px;
    background-color: #39aeb4;
}

As you can see, I tried to add some Z-Index properties to the menu but that didn't change anything.

Thanks for your help !