 of the body element, which is the ICB reduced by body's margins).">
<style>
div {
  writing-mode: vertical-rl;
  font-family: monospace;
  font-size: 20px;
  position: relative; /* to be a container for #red*/
}
:root { overflow: hidden; }
.spacer { /* using 5 spacers of 20vh each instead of a single large one, so
             that the line would wrap between spacers if it ends up being
             shorter thatn 100vh*/
  display: inline-block;
  height: calc(20vh - 0.1px); /*Using this instead of 20vh, t