body, html {
  height: 100%;
  margin: 0;
  padding: 0;
  height: 100vh;
  background-image: url('bg2.png');
  background-size: cover;
  background-repeat: no-repeat;
  background-position: center;
  display: flex;
  justify-content: center;
  align-items: center;
}

#boite {
  text-align: center;
  z-index: 2;
}

#btn1{
  border-radius: 50%;
}
#btn2 {
  position: relative;
  display: none;
  z-index: 3;
  transition: opacity 1s ease-in-out;
  right: 270px;
  border-radius: 50%;
  width: 100px;
  height: 50px;

}
#bg2 {
  z-index: 1;
}

#texte {
  opacity: 0;
  transition: opacity 2s ease-in-out;
  font-size: 24px;
  margin-bottom: 20px;
  color: white;
}

#texte.visible {
  opacity: 1;
}