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HTML 

              
                <article>
  <article-header>
    <h1>Creating a Slide Deck with Just HTML and CSS</h1>
  </article-header>
  <section>
    <h2>CSS Scroll Snap</h2>
    <p>Scroll snap allows us to create slides based on child elements of a scroll container.</p>
  </section>
  <section>
    <h2>Counting Slides with CSS Counters</h2>
    <p>We can use CSS counters to number the slides. This can be included in layouts.</p>
  </section>
  <section>
    <h2>Using CSS Grid to Create Layouts</h2>
    <p>CSS grid allows us to create slide layouts with ease.</p>
  </section>
</article>
!

CSS 

              
                /* Border-box all the things */
* {
  box-sizing: border-box;
}

/* Cover the whole screen */
html,
body {
  block-size: 100%;
}

/* This is the slide deck */
article {
  /* Cover the screen */
  block-size: 100%;
  /* Make it a flex container */
  display: flex;
  /* Make it a scroll container */
  overflow-x: scroll;
  /* Make inline scrolling snap */
  scroll-snap-type: x mandatory;
  /* Use inline axis for scrolling where supported */
  @supports (overflow-inline: scroll) {
    overflow-inline: scroll;
    scroll-snap-type: inline mandatory;
  }
  /* Set up a slide counter */
  counter-reset: slide;
}

/* These are the slides */
article > * {
  /* Fill the scroll container */
  flex: 0 0 100%;
  /* Scroll to the start of the slide */
  scroll-snap-align: start;
  /* Increment the slide counter */
  counter-increment: slide;
}

/* This is the counter */
article > ::before {
  /* Display the counter */
  content: counter(slide);
}

/* This is a cover layout for the first slide */
article > :first-child {
  display: grid;
  place-content: center;
  text-align: center;
  padding-inline: 4rem;
  font-size: clamp(1rem, 1rem + 2vw, 3rem);
  line-height: 1.3;
}

/******************************************************
 Presentational styles (not required for the technique) 
 ******************************************************/

:root {
  --foreground: #000;
  --background: #fff;
}

@media (prefers-color-scheme: dark) {
  :root {
    --foreground: #fff;
    --background: #000;
  }
}

body {
  margin: 0;
  font-family: Avenir Next, system-ui;
  background-color: var(--background);
  color: var(--foreground);
}

article {
  scrollbar-color: var(--foreground) transparent;
  scrollbar-width: thin;
}

/* Make each slide a grid layout */
article > * {
  position: relative;
  display: grid;
  grid-auto-flow: row;
  grid-template-rows: max-content;
  row-gap: 1rem;
  padding: 2rem;
  font-size: 1.5rem;
}

/* Style the slide counter */
article > ::before {
  position: absolute;
  inset-block-start: 1rem;
  inset-inline-end: 1rem;
  padding: 0.75rem;
  font-size: 1rem;
  font-weight: 700;
  font-variant: tabular-nums;
  line-height: 1;
  background-color: var(--foreground);
  color: var(--background);
  clip-path: circle();
}

/* Remove margin for slide content */
article > * > * {
  margin: 0;
}

/* For all none cover layouts set the heading size */
article > * + * > :first-child {
  font-size: 2em;
}

/* For the cover layout set the measure */
article > :first-child > :first-child {
  max-inline-size: 21ch;
}
!

JS
!
999px

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