html {
  box-sizing: border-box;
  width: 100%;
  height: 100vh;
}
@keyframes slideInFromTop {
  0% {
    opacity: 0;
    transform: translateY(-100%) rotateX(90deg);
  }
  90% {
    opacity: 1;
    transform: translateY(2.5%) rotateX(10deg);
  }
  100% {
    opacity: 1;
    transform: translateY(0) rotateX(0);
  }
}
body {
  margin: 0;
  width: 100%;
  height: 100vh;
  font-family: "Helvetica Neue", sans-serif;
  text-align: center;
  padding-top: 50px;
  background-color: #000000;
  position: relative;
  overflow: hidden;

  opacity: 0;
  animation: slideInFromTop 1s ease-in-out forwards;
  transform-origin: top;
}
/* la class quand on :hover les teaching <a> */
.teaching h1,
.teaching h2 {
  color: #333333;
}
h1 {
  padding: 15px 25px;
  color: #e5e4e4;
  z-index: 1;
  margin: auto;
  margin-bottom: 20px;
  width: fit-content;
}
h2 {
  padding: 15px 25px;
  color: #e5e4e4;

  z-index: 1;
  margin: auto;
  width: fit-content;
}
a {
  width: 220px;
  display: inline-block;
  margin: 40px 100px 20px;
  padding: 15px 30px;
  font-size: 20px;
  color: #fff;
  background-image: radial-gradient(
    circle 1292px at -13.6% 51.7%,
    rgba(0, 56, 68, 1) 0%,
    rgba(163, 217, 185, 1) 51.5%,
    rgba(255, 252, 247, 1) 88.6%
  );
  /*   background-size: 300%; */
  border: none;
  border-radius: 21px;
  text-decoration: none;
  transition: transform 0.3s, box-shadow 0.3s;
  z-index: 1;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
}
a:hover {
  transform: scale(1.05);
  box-shadow: 0 6px 20px rgba(0, 0, 0, 0.3);
}
#first-link:hover {
  background-image: linear-gradient(45deg, #ff7e5f, #feb47b);
  color: black;
  font-weight: bold;
}
#second-link:hover {
  background-image: linear-gradient(45deg, #00c6ff, #0072ff);
  color: black;
  font-weight: bold;
}
#third-link:hover {
  background-image: linear-gradient(45deg, #0055a4, #ffffff, #ef4135);
  color: black;
  font-weight: bold;
}
#fourth-link:hover {
  background-image: linear-gradient(
    45deg,
    #00247d,
    /* Blue */ #ffffff,
    /* White */ #cf142b,
    /* Red */ #ffffff,
    /* White */ #0335b4,
    /* Blue */ #ffffff,
    /* White */ #cf142b,
    /* Red */ #ffffff,
    /* White */ #00247d /* Blue */
  );
  color: black;
  font-weight: bold;
}
#background-video {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  object-fit: cover;
  z-index: -2;
  opacity: 0;
  transition: opacity 1s ease-in-out;
}

#background-video.visible {
  opacity: 1;
}

@media screen and (max-width: 800px) {
  body {
    padding-top: 25px;
  }
  a {
    margin: 14px 0;
  }
}