I was reading “Creative List Styling” on Google’s web.dev blog and noticed something odd in one of the code examples in the ::marker
section of the article. The built-in list markers are bullets, ordinal numbers, and letters. The ::marker
pseudo-element allows us to style these markers or replace them with a custom character or image.
::marker {
content: url('/marker.svg') ' ';
}
The example that caught my attention uses an SVG icon as a custom marker for the list items. But there’s also a single space character (" "
) in the CSS value next to the url()
function. The purpose of this space seems to be to insert a gap after the custom marker.
When I saw this code, I immediately wondered if there was a better way to create the gap. Appending a space to content
feels more like a workaround than the optimal solution. CSS provides margin
and padding
and other standard ways to space out elements on the page. Could none of these properties be used in this situation?
First, I tried to substitute the space character with a proper margin:
::marker {
content: url('/marker.svg');
margin-right: 1ch;
}
This didn’t work. As it turns out, ::marker
only supports a small set of mostly text-related CSS properties. For example, you can change the font-size
and color
of the marker, and define a custom marker by setting content
to a string or URL, as shown above. But the margin
and padding
properties are not supported, so setting them has no effect. What a disappointment.
Could it really be that a space character is the only way to insert a gap after a custom marker? I needed to find out. As I researched this topic, I made a few interesting discoveries that I’d like to share in this article.
Adding padding and margins
First, let’s confirm what margin
and padding
do on the
- and
- increases the gap after the list marker. The other three properties control the spacing to the left of the marker, in other words, the indentation of the list item.
Notice that even when the list item’s
padding-left
is0px
, there is still a minimum gap after the marker. This gap cannot be decreased withmargin
orpadding
. The exact length of the minimum gap depends on the browser.The first three properties push the entire list item (including the marker) to the right. The fourth property pushes only the list item’s content to the right. To sum up, the list item’s content is positioned at a browser-specific minimum distance from the marker, and this gap can be further increased by adding a
padding-left
to - .
Next, let’s see what happens when we position the marker inside the list item.
Moving the marker inside the list item
The
list-style-position
property accepts two keywords:outside
, which is the default, andinside
, which moves the marker inside the list item. The latter is useful for creating designs with full-width list items.The list marker is positioned inside the list item, so that the list item’s bottom border can extend to the left edge of the list box If the marker is now inside the list item, does this mean that
padding-left
on - no longer increases the gap after the marker? Let’s find out. On my test page, turn on
list-style-position: inside
via the checkbox. How are the fourpadding
andmargin
properties affected by this change?As you can see,
padding-left
on - now increases the spacing to the left of the marker. This means that we’ve lost the ability to increase the gap after the marker. In this situation, it would be useful to be able to add
margin-right
to the::marker
itself, but that doesn’t work, as we’ve established above.All four properties push the entire list item to the right. The minimum gap cannot be increased by standard means. Additionally, there’s a bug in Chromium that causes the gap after the marker to triple after switching to
inside
positioning. By default, the length of the gap is about one-third of the text size. So at a defaultfont-size
of16px
, the gap is about5.5px
. After switching toinside
, the gap grows to the full16px
in Chrome. This bug affects thedisc
,circle
, andsquare
markers, but not ordinal number markers.The following image shows the default rendering of outside and inside-positioned list markers across three major browsers on macOS. For your convenience, I’ve horizontally aligned all list items on their markers to make it easier to compare the differences in gap sizes.
Only Firefox maintains the same gap size between the two marker positioning modes. This can be considered a browser interoperability (interop) issue. To sum up, switching to
list-style-position: inside
introduces two problems. We can no longer increase the gap viapadding-left
on - , and the gap size is inconsistent between browsers.
Finally, let’s see what happens when we replace the default list marker with a custom marker.
Switching to a custom marker
There are two ways to define a custom marker:
list-style-type
andlist-style-image
propertiescontent
property on the::marker
pseudo-element
The
content
property is more powerful. For example, it allows us to use thecounter()
function to access the list item’s ordinal number (the implicitlist-item
counter) and decorate it with custom strings.Unfortunately, Safari doesn’t support the
content
property on::marker
yet (WebKit bug). For this reason, I’m going to use thelist-style-type
property to define the custom marker. You can still use the::marker
selector to style the custom marker declared vialist-style-type
. That aspect of::marker
is supported in Safari.Any Unicode character can potentially serve as a custom list marker, but only a small set of characters actually have “Bullet” in their official name, so I thought I’d compile them here for reference.
Character Name Code point CSS keyword • Bullet U+2022
disc
‣ Triangular Bullet U+2023
⁃ Hyphen Bullet U+2043
⁌ Black Leftwards Bullet U+204C
⁍ Black Rightwards Bullet U+204D
◘ Inverse Bullet U+25D8
◦ White Bullet U+25E6
circle
☙ Reversed Rotated Floral Heart Bullet U+2619
❥ Rotated Heavy Black Heart Bullet U+2765
❧ Rotated Floral Heart Bullet U+2767
⦾ Circled White Bullet U+29BE
⦿ Circled Bullet U+29BF
Note: The CSS
square
keyword does not have a corresponding “Bullet” character in Unicode. The character that comes closest is the Black Small Square (▪️) emoji (U+25AA
).Now let’s see what happens when we replace the default list marker with
list-style-type: "•"
(U+2022
Bullet). This is the same character as the default bullet, so there shouldn’t be any major rendering differences. On my test page, turn on thelist-style-type
option and observe any changes to the marker.As you can see, there are two significant changes:
- There is no longer a minimum gap after the marker.
- The bullet has become smaller, as if it were rendered at a smaller
font-size
.
According to CSS Counter Styles Level 3, the default list marker (
disc
) should be “similar to •U+2022
BULLET”. It seems that browsers increase the size of the default bullet to make it more legible. Firefox even uses a special font,-moz-bullet-font
, for the marker.The “Fonts” pane in Firefox’s DOM inspector reveals the special font. Can the small size problem be fixed with CSS? On my test page, turn on marker styling and observe what happens when you change the
font-size
,line-height
, andfont-family
of the marker.As you can see, increasing the
font-size
causes the custom marker to become vertically misaligned, and this cannot be corrected by decreasing theline-height
. Thevertical-align
property, which could easily fix this problem, is not supported on::marker
.But did you notice that changing the
font-family
can cause the marker to become bigger? Try setting it toTahoma
. This could potentially be a good-enough workaround for the small-size problem, although I haven’t tested which font works best across the major browsers and operating systems.You may also have noticed that the Chromium bug doesn’t occur anymore when you position the marker inside the list item. This means that a custom marker can serve as a workaround for this bug. And this leads me to the main problem, and the reason why I started researching this topic. If you define a custom marker and position it inside the list item, there is no gap after the marker and no way to insert a gap by standard means.
- There is no minimum gap after custom markers.
::marker
doesn’t supportpadding
ormargin
.padding-left
oninside
.
Summary
Here’s a summary of all the key facts that I’ve mentioned in the article:
- Browsers apply a default
padding-inline-start
of40px
to - There is a minimum gap after built-in list markers (
disc
,decimal
, etc.). There is no minimum gap after custom markers (string or URL). - The length of the gap can be increased by adding a
padding-left
to - Custom string markers have a smaller default size than built-in markers. Changing the
font-family
on::marker
can increase their size.
Conclusion
Looking back at the code example from the beginning of the article, I think I understand now why there’s a space character in the
content
value. There is just no better way to insert a gap after the SVG marker. It’s a workaround that is needed because no amount ofmargin
andpadding
can create a gap after a custom marker that is positioned inside the list item. Amargin-right
on::marker
could easily do it, but that is not supported.Until
::marker
adds support for more properties, web developers will often have no choice but to hide the marker and emulate it with a::before
pseudo-element. I had to do that myself recently because I couldn’t change the marker’sbackground-color
. Hopefully, we won’t have to wait too long for a more powerful::marker
pseudo-element.
elements. I’ve created a test page for this purpose. Drag the relevant sliders and observe the effect on the spacing on each side of the list marker. Tip: Use the Reset button liberally to reset all controls to their initial values.
Note: Browsers apply a default padding-inline-left
of 40px
to
- and
elements. The logical padding-inline-left
property is equivalent to the physical padding-left
property in writing systems with a left-to-right inline direction. In this article, I’m going to use physical properties for the sake of simplicity.
As you can see, padding-left
on