CSS only slideshow

The HTML is one section per slide.

HTML
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<section>
  <h1>Slide 1</h1>
</section>
<section>
  <h1>Slide 2</h1>
</section>
CSS
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/** Import Fonts */
@import url('https://fonts.googleapis.com/css2?family=Ubuntu:wght@400;500;700&display=swap');

/** vars */
:root {
  /** typography */
  --font-family: 'Ubuntu', -apple-system, BlinkMacSystemFont, avenir next, avenir, segoe ui, helvetica neue, helvetica, Cantarell, Ubuntu, roboto, noto, arial, sans-serif;
  --text-base-size: 8vw;

  /** colors */
  --main-bg-color: black;
  --main-font-color: white;
  --accent-bg-color: white;
  --accent-font-color: black;
  --text-shadow: 0 0 10px #93c5fd;
}

/* reset */
*, *::before, *::after {
  box-sizing: border-box;
}
* {
  margin: 0;
}
img, picture, video, canvas, svg {
  display: block;
  max-width: 100%;
  max-height: 100%;
}

/** typography */
body {
  font-family: var(--font-family);
  color: var(--main-font-color);
  font-size: calc(var(--text-base-size) - 4.5vw)
}
h1, h2, h3 {
  text-shadow: var(--text-shadow);
}
h1 {
  font-size: var(--text-base-size);
  font-weight: bold;
  padding: 10px 0;
}
h2 {
  font-size: calc(var(--text-base-size) - 2vw);
  font-weight: medium;
  padding: 5px 0;
}
h3 {
  font-size: calc(var(--text-base-size) - 4vw);
}
a {
  text-decoration: underline;
  color: inherit;
}

/** slide structure */
html {
  scroll-snap-type: y mandatory;
  background-color: var(--main-bg-color);
}
section {
  block-size: 100vh;
  scroll-snap-align: center;
  scroll-snap-stop: always;
  overflow: hidden;
  display: flex;
  flex-direction: column;
  justify-content: center;
  place-items: center;
  position: relative;
}
section.accent {
  background-color: var(--accent-bg-color);
  color: var(--accent-font-color);
}
section.bw {
  background-color: white;
  color: black;
}
section.wb {
  background-color: black;
  color: white;
}
section .sides {
  display: flex;
}
section .sides div {
  padding: 20px;
  align-items: center;
  display: flex;
}

/** video and background image styles */
iframe {
  width: 100%;
  height: 100%;
  border: none;
  overflow: hidden;
}
img.background, img.cover {
  position: absolute;
  top: 0;
  width: 100%;
  height: 100%;
  z-index: -1;
}

/** print style */
@media print {
  @page {
    margin: 0.5in;
    size: landscape;
  }
  section {
    width: 10in;
    height: 7.5in;
    page-break-after: always;
    background-color: transparent !important;
    color: black !important;
    border: 1px solid #666;
  }
  section:last-of-type {
    page-break-after: avoid;
  }
  h1, h2 {
    text-shadow: none !important;
  }
  a::after{
    content: "\A(" attr(href) ") ";
    white-space: pre-line;
    font-size: 18px;
    font-weight: normal;
  }
  img.background {
    display: none;
  }
}