styles.css

:root {
  --lightbox-width: 90vw;
  --lightbox-height: 90vh;
}

body {
  padding: 0;
  margin: 0;
  box-sizing: content-box;
  overflow: hidden;
}

article {
  width: 800px;
  margin: auto;
}

#overlay {
  position: absolute;
  width: 100%;
  height: 100%;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  background-color: rgba(0, 0, 0, 0.85);
  z-index: 100;
  cursor: not-allowed;
}

.lightbox-container {
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  margin: auto;
  overflow: hidden;
  min-width: var(--lightbox-width);
  max-width: var(--lightbox-width);
  min-height: var(--lightbox-height);
  max-height: var(--lightbox-height);
  z-index: 200;
  cursor: not-allowed;
}

.lightbox-slide {
  display: flex;
  flex-direction: row;
  flex-wrap: nowrap;
  /* background-color: greenyellow; */
}

.image-wrapper {
  min-width: var(--lightbox-width);
  max-width: var(--lightbox-width);
  min-height: var(--lightbox-height);
  max-height: var(--lightbox-height);
  display: flex;
  flex-direction: row;
  flex-wrap: nowrap;
  align-items: center;
  /* background-color: pink; */
}

.lightbox-image {
  margin: auto;
  /* background-color: yellow; */
}

.noselect {
  -webkit-touch-callout: none; /* iOS Safari */
  -webkit-user-select: none; /* Safari */
  -khtml-user-select: none; /* Konqueror HTML */
  -moz-user-select: none; /* Old versions of Firefox */
  -ms-user-select: none; /* Internet Explorer/Edge */
  user-select: none; /* Non-prefixed version, currently
                        supported by Chrome, Edge, Opera and Firefox */
}

#prevBtn {
  position: absolute;
  top: 50%;
  z-index: 300;
  left: 5%;
  font-size: 2rem;
  padding: 1rem;
  cursor: pointer;
  font-weight: 900;
  color: #fff;
  background-color: rgba(0, 0, 0, 0.85);
}

#prevBtn:active {
  background-color: rgba(0, 0, 0, 0.75);
}

#nextBtn {
  position: absolute;
  top: 50%;
  z-index: 300;
  right: 5%;
  font-size: 2rem;
  padding: 1rem;
  cursor: pointer;
  font-weight: 900;
  color: #fff;
  background-color: rgba(0, 0, 0, 0.85);
}

#nextBtn:active {
  background-color: rgba(0, 0, 0, 0.75);
}

.hidden {
  visibility: visible;
}