input:invalid+span:after {
    position: absolute; content: '✖';
    padding-left: 5px;
    color: #8b0000;
  }
  
  input:valid+span:after {
    position: absolute;
    content: '✓';
    padding-left: 5px;
    color: #009000;
  }
#prenom {
  position: relative;
}
#name {
  position: relative;
}