css渐变色

.dialog-mask {
  width: 100%;
  height: 100%;
  background: rgba(0, 0, 0, 0.8);
  position: fixed;
  top: 0;
  bottom: 0;
  z-index: 888;
  opacity: 0;
}


.dialog-mask.active {
  opacity: 1;
  transition: all 0.3s;
}