css

/* viewportの横幅と高さの実数値を取得する */

@property --viewport-w {
  syntax: "<length>";
  inherits: true;
  initial-value: 100vw;
}
@property --viewport-h {
  syntax: "<length>";
  inherits: true;
  initial-value: 100vh;
}

body {
  --calculated-viewport-w: tan(atan2(var(--viewport-w), 1px));
  --calculated-viewport-h: tan(atan2(var(--viewport-h), 1px));
  background-color: orange;
}
body:before {
  content: counter(w) "x" counter(h);
  counter-reset: h var(--calculated-viewport-h) w var(--calculated-viewport-w);
}