.entete_description{ /* Le bas de l'entête */
    margin-top: 400px;
    position: relative;
    display: block;
    z-index: 3;
    padding: 1.25rem;
    display: flex;
    align-items: flex-start;
    align-content: space-between;
}

.entete_description h1 span{ /* Titre de la page */
    color: black;
    display: block;
    line-height: 1;
    font-size: 35;
}

.button{ /* Bouton de la div droite " Démo" */
    margin-bottom: 100px;
    height: 60px;
}

button::after {
    -webkit-transition: all 20s;
    -moz-transition: all 20s;
    transition: all 0.8s;
}

.entete_description_bouton { /* Contenu du bouton */
    margin-top: 40px;
    margin-left: auto;
    margin-right: auto;
    background: white;
    border: 2px solid #FFFFFF;
    color: black;
    display: block;
    font-size: 20;
    font-weight: bold;
    padding: 20px 60px;
    position: relative;
    cursor: pointer;
    z-index: 1;
}

button::before, button::after { /* Couleur du backround par dessus */
    background: black;
    content: '';
    position: absolute;
    z-index: -2;
}

.entete_description_bouton:hover {
    color: white;
}

.entete_description_bouton::after {
    height: 100%;
    left: 0;
    top: 0;
    width: 0;
}
    
.entete_description_bouton:hover:after {
    width: 100%;
 }