body {
  margin: 0;
  height: 100vh;
  font: normal 75% Arial, Helvetica, sans-serif;
}

canvas {
  display: block;
  vertical-align: bottom;
}

/* ---- particles.js container ---- */
#particles-js {
  position: fixed; /* <--- utilise fixed au lieu de absolute */
  width: 100%;
  height: 100%;
  top: 0;
  left: 0;
  background-color: rgb(0, 0, 0);
  background-image: url("");
  background-repeat: no-repeat;
  background-size: cover;
  background-position: 50% 50%;
  z-index: 0;
}

.overlay {
  position: relative;
  z-index: 1;
  display: flex;
  justify-content: center;
  align-items: center; 
  color: white;
  font-size: 2rem;
  height: 100vh;
}

.butn * {
  margin: 0;
}

.butn {
  margin: 0 20px 20px 20px;
}
.butn {
  cursor: pointer; /* pour le curseur "clic" */
}

.butn:link,
.butn:visited,
.butn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: 100%;
  text-transform: uppercase;
  text-decoration: none;
  background-color: #5e16bd;
  background-image: linear-gradient(90deg, #501aa8, #870de8);
  padding: 10px;

  margin-right: 13px;
  border-radius: 4px;
  border: none;
  color: #fff;
  position: relative;
  overflow: hidden;
  transition: all 0.3s ease-in-out;
}

.butn span {
  padding: 7px;
  z-index: 20;
}

.butn::before {
  background: #fff;
  content: "";
  height: 155px;
  opacity: 0;
  position: absolute;
  top: -50px;
  transform: rotate(35deg);
  width: 50px;
  transition: all 3000ms cubic-bezier(0.19, 1, 0.22, 1);
}

.butn::after {
  background: #fff;
  content: "";
  height: 20rem;
  opacity: 0;
  position: absolute;
  top: -50px;
  transform: rotate(35deg);
  transition: all 3000ms cubic-bezier(0.19, 1, 0.22, 1);
  width: 8rem;
}

.butn__new::before {
  left: -50%;
}

.butn__new::after {
  left: -100%;
}

.butn:hover,
.butn:active {
  transform: translateY(-3px);
  color: #fff;
  box-shadow: 0 10px 20px 0 rgba(0, 0, 0, 0.3);
}

.butn__new:hover::before {
  left: 120%;
  opacity: 0.5;
}

.butn__new:hover::after {
  left: 200%;
  opacity: 0.6;
}