popup.css

* {
    user-select: none;
}

body {
    background-color: rgb(65 65 65);
    padding: 5px;
}

button, span {
    margin: 4px 0px;
    padding: 5px 10px;
    border-radius: 4px;
    outline: none;
    background-color: hsl(0deg 0% 46%);
    border: 2px solid hsl(0deg 0% 46%);
    font-family: 'Roboto', sans-serif;
    font-weight: 500;
    text-transform: uppercase;
}

button:hover {
    opacity: .7;
}

button:active {
    opacity: 1;
    color: white;
    background-color: rgb(65 65 65);
    border: 2px solid hsl(0deg 0% 46%);
}

.prevnextbtn {
    display: inline-block;
}

.prevnextbtn > button {
    padding: 8px 10px;
}

.fas {
    font-size: 19px;
}

.fa-image {
    position: relative;
    top: 2px;
    font-size: 25px;
    margin-right: 2px;
}

.thumbnailcontainer {
    width: 356px;
    height: 200px;
    background-color: rgb(48, 48, 48);
    border-radius: 15px;
    overflow: hidden;
    box-shadow: 5px 5px 10px gray;
}
.thumbnailinpopup {
    width: inherit;
    height: inherit;
    transition: .3s;
}
.thumbnailinpopup:hover {
    cursor: pointer;
    opacity: .4;
}

span {
    display: inline-block;
    width: 52px;
    text-align: center;
    padding: 10px 1px;
    font-weight: 700;
    letter-spacing: 1px;
    position: relative;
    bottom: 3px;
    color: white;
}