.overlay{
    opacity:0.8;
    background-color:#ccc;
    position: absolute;
    width:100%;
    height:100%;
    top:0px;
    left:0px;
    z-index:1000;

    position: absolute; /* Sit on top of the page content */
    width: 100%; /* Full width (cover the whole page) */
    height: 100%; /* Full height (cover the whole page) */
    top: 0; 
    left: 0;
    right: 0;
    bottom: 0;
    background-color: rgba(0,0,0,0.5); /* Black background with opacity */
    z-index: 2; /* Specify a stack order in case you're using a different order for other elements */
    cursor: pointer; /* Add a pointer on hover */
}
.loader {
  border: 16px solid #f3f3f3;
  border-radius: 50%;
  border-top: 16px solid #3498db;
  border-bottom: 16px solid #3498db;
  width: 120px;
  height: 120px;
  -webkit-animation: spin 2s linear infinite; /* Safari */
  animation: spin 2s linear infinite;

  /*posicion*/
  position:absolute; /*it can be fixed too*/
    left:0; right:0;
    top:0; bottom:0;
    margin:auto;

    /*this to solve "the content will not be cut when the window is smaller than the content": */
    max-width:100%;
    max-height:100%;
    overflow:auto;
}

/* Safari */
@-webkit-keyframes spin {
  0% { -webkit-transform: rotate(0deg); }
  100% { -webkit-transform: rotate(360deg); }
}

@keyframes spin {
  0% { transform: rotate(0deg); }
  100% { transform: rotate(360deg); }
}