#slider {
    position: relative;
    display: inline-grid;
    align-items: center;
    margin: auto;
}
#precedente, #suivante {
    position: absolute;
    font-size: 40px;
    color:hwb(180 94% 5% / 0.973);
    cursor: pointer;
    opacity: 0;
    transition: opacity 0,3s;
}
#precedente {
    left: 0;
}
#suivante {
    right: 0;
}
#slider:hover #precedente, #slider:hover #suivante {
    opacity: 1; 
}