style.css

body{
  margin: 0;
}
#sliders {
  height: 400px;
  width: 60%;
  overflow: hidden;
  margin: 0 auto;
  position: relative;
}

.gallery-header {
  display: none;
}

.slider-item {
  display: none;
}

.img-thumbnail {
  cursor: pointer;
}

.added {
  border: 2px solid #1e1743;
  border-radius: 5px;
}

img {
  height: 400px;
  object-fit: cover;
}

.prev-next {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translateX(-50%) translateY(-50%);
  cursor: pointer;
}

.prev, .next {
  background-color: transparent;
  padding: 8px 10px;
  color: #fff;
}

.dot {
  background-color: rgb(163, 156, 156);
  height: 10px;
  width: 10px;
  border-radius: 50%;
  cursor: pointer;
  margin: 0 3px;
}

.main {
  display: none;
}

@media (max-width: 767px) {
  .justify-content-around.align-items-center.mt-3.gallery-header.mb-2 {
    flex-direction: column;
  }
  #sliders {
    height: 300px;
    width: 90%;
  }
}

/* onloader */
#loader {
  position: absolute;
  left: 50%;
  top: 50%;
  z-index: 1;
  width: 100px;
  height: 100px;
  margin: -76px 0 0 -76px;
  border: 16px solid #f3f3f3;
  border-radius: 50%;
   border-top: 16px solid #007bff;
  border-bottom: 16px solid #007bff;
  
  -webkit-animation: spin 2s linear infinite;
  animation: spin 2s linear infinite;
}

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

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

/* Add animation to "page content" */
.animate-bottom {
  position: relative;
  -webkit-animation-name: animatebottom;
  -webkit-animation-duration: 1s;
  animation-name: animatebottom;
  animation-duration: 1s;
}

@-webkit-keyframes animatebottom {
  from { bottom:-100px; opacity:0 } 
  to { bottom:0px; opacity:1 }
}

@keyframes animatebottom { 
  from{ bottom:-100px; opacity:0 } 
  to{ bottom:0; opacity:1 }
}

#myDiv {
  display: none;
  text-align: center;
}