body {
  //background-image: url('http://www.rodrigodiaz.fr/images/background_cha.jpg');
  background-repeat: no-repeat;
  background-attachment: fixed;
}

.presentation {
  //display: none;
  background-color: white;
  box-shadow: 0px 0px 10px 1px rgba(0, 0, 0, 0.1);
  height: 0px;
  width: 100%;
  padding-bottom: 20%;
}

.presentation p {
  font-size: 1.3vw;
  color: black ; 
  padding-top: 3% ;
  padding-right: 5%;
  padding-left: 25%;
}

@media (min-width: 768px) {
  
  .presentation {
  background-image: url('http://rodrigodiaz.fr/images/profil_cha.jpg');
  background-size: contain;
  background-repeat: no-repeat;
  }
  
  .presentation img {
    display: none;
  }
  
}

@media screen and (min-width: 1200px) {
  .presentation p {
    font-size: 17px;
  }
}

@media (max-width: 768px) {
  .presentation {
    width: 99%;
    height: 100%;
    margin: 2px;
    margin-top : 40px;
    padding-bottom: 5%;
    background-image: none;
  }
  
  .presentation img {
  width: 100%;
  float: top;
  }

.presentation p {
  padding-left: 20px ;
  font-size: 1em;
  }
}