<div>
  <p>文字を縦書きにしたいです</p>
  <p>縦書きにしたり横書きにしたり日本語って難しいですね</p>
</div>
div {
  -webkit-writing-mode: vertical-rl;
      -ms-writing-mode: tb-rl;
          writing-mode: vertical-rl;
}

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