JSFiddle - React, Tailwind, and code Playground

HTML

<div class="block-vertical">
    <div class="block-vertical-middle">Блок по центру страницы</div>
</div>

CSS

html,
body {
  position: relative;
  min-height: 100%;
}

html {
  height: 100%;
}

.block-vertical {
  position: fixed;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  width: 100%;
  height: 100%;
  font-size: 0.001px;
  text-align: center;
}

.block-vertical:before {
  content: '';
  display: inline-block;
  height: 100%;
  vertical-align: middle;
}

.block-vertical-middle {
  display: inline-block;
  width: 80%;
  height: 70%;
  max-width: 100%;
  font-size: 14px; /* font-size: 1rem; */
  vertical-align: middle;
  border: 1px solid #f00;
}