/* css du bouton */


a {
 display: block;
 
   margin : auto;
width: auto; /* largeur */
   height: auto; /* hauteur */
  display: flex;
  justify-content: center;
  align-items: center;
  text-decoration: none;
  text-align:center;
  font-weight: bold;
  color: red;
  font-family: sans-serif;
  font-size: 1em;
 
  border-radius: 20px;
  box-shadow: 5px 10px 20px #888888; /* ombre */
  border: 2mm ridge rgba(25, 300, 50, .9);
  background: silver;  /* couleur du fond */
  padding: 0.5em  ;
  position: relative;
 
  overflow: hidden;
  z-index:0
    
}

a:before {
  content: '';
  background-color: yellow;
  top: 0;
  left: 0;
  width: 50px;
  height: 100%;
  
  position: absolute;
  z-index: -1;
  transform: skew(-50deg);
  animation: moving 5s  infinite linear;
  animation-direction: alternate;
  transition: all 0.1s;
}

@keyframes moving {
  from { left: -120px; }
  
  to { left: 100%; }
}

a:hover::before {
  width: 100%;
  transform: skew(0deg);
  animation: none;
}