#fontspecial {
      font-family: Arial, sans-serif;
}
#maintuto {
  display: block;
}
#titre{
      text-align: center;
}
#polarity tbody {
      display: none;
    }
#penumbra tbody {
      display:none;
    }
#symmetry tbody {
      display: none;
    }
#distribution tbody {
      display:none;
    }
#go{text-align: center;
      font-size: 20px;
}
footer{
     text-align: center; 
}
.center {
  display: block;
  margin-left: auto;
  margin-right: auto;
  width: 50%;
  width: 250px;
}