.connexion_div {
  height: 300px;
  text-align: center;
  margin: 20px;
}

.connexion_div::before {
  content: '';
  display: inline-block;
  height: 100%; 
  vertical-align: middle;
  margin-right: -0.25em;
}

.connexion_under_div {
    background-color: white;
    text-align: center;
    max-width: 1200px;
    border-radius: 30px;
    display: inline-block;
    vertical-align: middle;
    padding: 15px;
}

.connexion_under_div > h2, form, button, div, p {
    color: black;
    padding: 5px;
}

.connexion_div label {
    color: black;
}