#button3
{
    color: #24A19C;
}

#button3:after {
    display:block;
    content: '';
    border-bottom: solid 2px #24A19C;  
    transform: none;
  }

#conteneur
{
    display: flex;
    flex-direction: column;
    margin: 20px 0 0 0;
    padding: 0 18%;
}