imageSlider.css

* {
    box-sizing: border-box;
    padding: 0;
    margin: 0;
}

body {
    width: 100%;
    height: 757px;
    background: #ebd687;
    display: flex;
    justify-content: center;
    align-items: center;
}

#container {
    display: flex;
    justify-content: space-evenly;
    align-items: center;
    flex-direction: column;
    width: 70%;
    height: 757px;
    background: #ffe37d;
    /* border: 3px solid #fde585; */
    box-shadow: 0 0 5px #bbb, 0 0 5px #bbb;
}

#output {
    width: 100%;
    height: 500px;
    background-image: #fadb6a;
    /* box-shadow: 0 0 15px 3px #888, 0 0 15px 3px #888; */
    box-shadow:
    0px 3px 8px -3px rgba(50, 50, 50, 0.75),
    0px -3px 8px -3px rgba(50, 50, 50, 0.75);
}

#btnNext, #btnLast {
    padding: 10px 15px;
    background: #ffe37d;
    border: none;
    font-size: 40px;
    cursor: pointer;
    color:snow;
    font-weight: bold;
    text-shadow: 0 0 3px #666, 0 0 3px #666;
}

#btnNext:hover, #btnLast:hover {
    text-shadow: 0 0 5px dodgerblue, 0 0 5px dodgerblue;
}

@media screen and (max-width: 1100px){
    #container {
        width: 75%;
    }
}

@media screen and (max-width: 950px){
    #container {
        width: 80%;
    }
}

@media screen and (max-width: 800px){
    #container {
        width: 85%;
    }
}

@media screen and (max-width: 600px){
    #container {
        width: 90%;
    }
}