Lost custom css style when downloading as reveal.js slides html

[lemuellew]

I put h1 tag on the top in rise.css, the style lost when downloading as reveal.js slides html

h1 {
  position: fixed;
  top: 0;
}

[lemuellew]

When slide presentation, h1 to the top will have a delay, the experience is bad :( https://streamable.com/e/lnjt75