.carousel-item{
    position: relative;
  
}
.carousel-item::after{
content:"";
display: block;
position: absolute;
top: 0;
bottom: 0;
left: 0;
right: 0;
background: linear-gradient(to right ,rgba(0, 0, 0, 0.6),rgba(0, 0, 0, 0.2));
}
.carousel-caption{
    width: 80%;
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    z-index: 10;
    margin: 0px auto;
}