css-xmatch

scroll-match

Prototype Demo at codepen. This idea come from css-element-queries

[x-scroll-match="y=0"] {
  // when scroll is at top
}

// or: body[x-scroll-match="y<=50vh"] .go-top {
body:not([x-scroll-match="y>50vh"]) .go-top {
  display: none;
}