body {
    background-position: center center;
    transition: .4s ease;
}
body::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100vh;
    background-color: rgba(0, 0, 0, 0.7);
    z-index: -1;
}    

#app {
   display: flex;
   position: relative;
}

.slider-area {
    position: relative;
    width: 70vw;
    height: 70vh;
    z-index: 1;
}

.slider-area .slider {
    position: absolute;
    opacity: 0;
    width: 100%;
    height: 100%;
    background-position: center center;
    transition: .4s ease;
}

.slider-area .slider.active {
    opacity: 1;
}

.btn {
    position: absolute;
    color: white;
    border: 2px solid orange;
    font-size: 3em;
    padding: .5em;
    top: calc(50% - 1em);
}
.btn:hover {
    cursor: pointer;
}

#prev_btn {
    left: -1.7em;
}
#next_btn {
    right: -1.7em;
}