How to make text run top-to-bottom in CSS?

To make the letters top-to-bottom while keeping their normal orientation, like this:

F

O

O

HTML:

<div class="toptobottom">letters</div>

CSS:

.toptobottom{
  width: 0;
  word-wrap: break-word;
}

word-wrap allows words to be broken in the middle, so this will make the letters top-to-bottom. It's also really well supported: https://developer.mozilla.org/en-US/docs/CSS/word-wrap

Having your text run along vertical lines WITHOUT HACKS

writing-mode

CSS writing-mode attribute lets your text run vertically.

.traditional-vertical-writing
{
  writing-mode: vertical-rl;
}

<p class="traditional-vertical-writing">
  This text runs vertically.<br>
  『只是』 （(but the thing is)），since Latin alphabets are not for vertical writing,
  not only the lines but each of the non-vertical-writing letters also gets rotated.<br>
  0123456789
</p>

text-orientation

If you don't want non-vertical-writing letters to rotate themselves in vertical lines, you may use CSS text-orientation attribute as well.

.vertical-writing
{
  writing-mode: vertical-rl;
  text-orientation: upright;
}

<p class="vertical-writing">
  This text runs vertically.<br>
  『それに』 （(and in addition)）、now you don't have to turn your head 90 degrees clockwise
  to read these non-vertical-writing letters!<br>
  0123456789
</p>

And if you’re to do some tate-chuu-yoko^[1][2][3] (a bit of horizontal writing while writing vertically),

consider using text-combine-upright.