.div_index {
  background-color: #000000;
 background-image: linear-gradient(rgba(0, 0, 0, 0.6), rgba(0, 0, 0, 0.6)), url(images/PSA-vue-aerienne1.jpg);
    left: 0;
    top: 0;
width: 100%;
 min-height: 100vh;
  margin: 0;
  padding: 0;
  background-position: center;
  background-size: cover;
  color: #ffffff;
  text-align: center;
}

.h1_index{
font-size:50px;
font-weight: bold;
}

.p_index{
font-size:25px;
}

.button_index{
position: relative;
top: 15%;
left: 20%;
text-decoration:  none;
}