列出標記和字符串樣式

Lists—we’ve all worked with them in one form or another. I’m talking about HTML’s

and

. Much of the time, because we desire styling control, we turn off the list’s markers completely with list-style-type: none, and start styling from there. Other times, we choose from a very limited set of unordered list markers, such as disc, circle, or square; or a (much) wider range of ordered list markers. We might even, from time to time, supply the URL of an image to be used.

But what if we want to style the markers differently than the contents of the list items? That’s always been difficult at best. Now, thanks to the ::marker pseudo-element, it’s a whole lot easier. You don’t get the full range of CSS to apply to the markers, but there’s still a great deal that can be done.

::marker is available in Firefox and, thanks to work by Igalia, Chrome as well.

Consider this list:

By default, that will yield an ordered list numbered from 1 to 5, using Arabic numerals (1, 2, 3, etc.), each followed by a dot (period), all of which will match the text contents in font face, size, style, color, and so on.

If you had a design direction that required making the numbers smaller or a different color, you’d have to manually create that effect by suppressing the markers and using the ::before pseudo-element and CSS counters and negative text indenting and… well, it would take a scientist to explain it all.

Enter ::marker. Add these styles to the above list, and you’ll get the result shown after.

That’s all you need!

Before you go tearing off to rewrite all your CSS, though, beware: the properties you can apply via ::marker are fairly limited at the moment. As of February 2021, the properties that markers should recognize are:

• All font properties (font-face, font-size, etc.)
• The white-space property
• The color property
• The internationalization properties text-combine-upright, unicode-bidi, and direction
• The content property
• All animation and transition properties

There are some additions in some browsers, but almost all of the additions relate to text styling, not the box model. So if you were thinking you could put all your list numbers into circles with shaded backgrounds, ::marker won’t get you there—you’ll have to return to the hackfest of ::before generated content. For now, anyway: the specification explicitly says more properties may be permitted for ::marker in the future.

There’s also a limitation around white-space, which has rendering bugs in varying browsers. Chrome, for example, treats all whitespace in markers as white-space: pre as the specification says, but won’t let you change it. This should be fixed when Chrome’s LayoutNG (Next Generation) ships, but not until then. Firefox, on the other hand, ignores any white-space values, and treats whitespace like normal-flow text by default.

With those limits in mind, you can still jazz up your markers with the content property. Instead of numbers followed by a period, you can put each number in brackets with a combination of counters and strings.

Note the space after the closing bracket in the content value. That’s included to provide a little bit of space between the marker and the list content. Ordinarily you might think to use a marking or padding, but as we saw earlier, those properties can’t be applied with ::marker. Which is frustrating! Also note the CSS counter list-item. That wasn’t defined anywhere else in the CSS—it’s a built-in counter that all browsers (that understand CSS counters) use to count list items, like those in ordered lists. You can use it in your CSS as well!

If all you want to do is change the text content of a list marker and don’t care about changing any of its styles, you can do that with ::marker, or you can do it with the new cross-browser support for string values on the list-style-type property.

li.warning {
  list-style-type:"⚠";
}

So that’s what’s new in the world of list markers. It might not be something you need to do often, but if you ever do, it’s good to know that the capabilities in this area have increased, and stand to be even better in the future. Let us know if you come up with some clever markers!

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