.sous-menu {
    width: 100%;
    text-align: left;
    background-color: white;
    border-radius: 2px;
    overflow: hidden;
    max-height: 0;
}

.sous-menu > li > a {
    height: 50px;
    padding-left: 20px;
    width: 100%;
    align-items: center;
    display: flex;
}

.sous-menu > li:hover {
    background-color: red;
}

.sous-menu > li:hover > a {
    color: white;
}

@keyframes rotationFleche {
    0% {
        transform: rotate(0deg);
    }
    100%{
        transform: rotate(90deg);
    }
}

.menu-deroulant:hover > a:after{
    animation: rotationFleche 0.2s linear forwards;
}

@keyframes apparitionSousMenu {
    0% {
        box-shadow: 0px 3px 3px 1px rgba(0,0,0,0);
        border-top: 3px solid #2169EC;
    }
    30% {
        box-shadow: 0px 3px 3px 1px rgba(0,0,0,0.3);
    }
    100% {
        max-height: 50em;
        border-top: 3px solid #2169EC;
        box-shadow: 0px 3px 3px 1px rgba(0,0,0,0.3);
    }
}
.menu-deroulant:hover > .sous-menu {
    animation: apparitionSousMenu 1s forwards;
}