css/css-contain/contain-html-w-m-001.html

<!doctype html>
<html lang=en>
  <meta charset=utf-8>
  <title>CSS-contain test: layout containment on html prevents writing-mode propagation</title>
  <link rel="author" title="Florian Rivoal" href="https://florian.rivoal.net">
  <meta name=flags content="">
  <meta name=assert content="layout containment on html prevents writing-mode propagation">
  <link rel="match" href="reference/contain-body-w-m-001-ref.html">
  <link rel=help href="https://drafts.csswg.org/css-contain-1/#contain-property">

<style>
html::before {
    content: "";
    width: 100px;
    height: 100px;
    background: orange;
    display: block;
}
p { writing-mode: horizontal-tb; margin: 0;}
body {
    margin: 0;
    width: 200px;
    height: 200px;
    writing-mode: vertical-rl;
}
html {
    contain: layout;
}
</style>

<p>Test passes if the orange square is in the upper-left corner.