* {
  padding: 0;
  margin: 0;
  list-style: none;
}

#slider {
  margin: 10px;
  width: 800px;
  height: 300px;
  overflow: hidden;
  position: relative;
}

.slide {
  opacity: 1;
  transition: opacity 0.8s;
  position: absolute;
}

button {
  font-size: 64px;
  color: white;
  background: transparent;
  border: none;
  outline: none;
  cursor: pointer;
  position: absolute;
  top: 110px;
  transition-duration: 0.3s;
}

#next {
  left: 760px;
}

#previous {
  left: 20px;
}

button:hover {
  color: lightgreen;
}

ul {
  position: absolute;
  left: 40%;
  bottom: 20px;
  display: flex;
  justify-content: space-between;
  width: 120px;
}

.thumbnail {
  width: 20px;
  height: 20px;
  background-color: rgba(255, 255, 255, 0.7);
  border-radius: 50%;
  cursor: pointer;
  transition: background-color 0.3s;
}

.thumbnail:hover,
.active {
  background-color: lightgreen;
}