Implementation
There are three different implementations: pseudo-elements, pseudo-classes, and nothing.
- WebKit, Blink (Safari, Google Chrome, Opera 15+) and Microsoft Edge are using a pseudo-element:
::-webkit-input-placeholder. [Ref]
- Mozilla Firefox 4 to 18 is using a pseudo-class:
:-moz-placeholder (one colon). [Ref]
- Mozilla Firefox 19+ is using a pseudo-element:
::-moz-placeholder, but the old selector will still work for a while. [Ref]
- Internet Explorer 10 and 11 are using a pseudo-class:
:-ms-input-placeholder. [Ref]
- April 2017: Most modern browsers support the simple pseudo-element
::placeholder [Ref]
Internet Explorer 9 and lower does not support the placeholder attribute at all, while Opera 12 and lower do not support any CSS selector for placeholders.
The discussion about the best implementation is still going on. Note the pseudo-elements act like real elements in the Shadow DOM. A padding on an input will not get the same background color as the pseudo-element.
CSS selectors
User agents are required to ignore a rule with an unknown selector. See Selectors Level 3:
a group of selectors containing an invalid selector is invalid.
So we need separate rules for each browser. Otherwise the whole group would be ignored by all browsers.
::-webkit-input-placeholder { /* WebKit, Blink, Edge */
color: #909;
}
:-moz-placeholder { /* Mozilla Firefox 4 to 18 */
color: #909;
opacity: 1;
}
::-moz-placeholder { /* Mozilla Firefox 19+ */
color: #909;
opacity: 1;
}
:-ms-input-placeholder { /* Internet Explorer 10-11 */
color: #909;
}
::-ms-input-placeholder { /* Microsoft Edge */
color: #909;
}
::placeholder { /* Most modern browsers support this now. */
color: #909;
}
<input placeholder="Stack Snippets are awesome!">
Usage notes
- Be careful to avoid bad contrasts. Firefox's placeholder appears to be defaulting with a reduced opacity, so needs to use
opacity: 1 here.
- Note that placeholder text is just cut off if it doesn’t fit – size your input elements in
em and test them with big minimum font size settings. Don’t forget translations: some languages need more room for the same word.
- Browsers with HTML support for
placeholder but without CSS support for that (like Opera) should be tested too.
- Some browsers use additional default CSS for some
input types (email, search). These might affect the rendering in unexpected ways. Use the properties -webkit-appearance and -moz-appearance to change that. Example:
[type="search"] {
-moz-appearance: textfield;
-webkit-appearance: textfield;
appearance: textfield;
}
It’s a holdover from the Netscape days:
Missing digits are treated as 0[...]. An incorrect digit is simply interpreted as 0. For example the values #F0F0F0, F0F0F0, F0F0F, #FxFxFx and FxFxFx are all the same.
It is from the blog post A little rant about Microsoft Internet Explorer's color parsing which covers it in great detail, including varying lengths of color values, etc.
If we apply the rules in turn from the blog post, we get the following:
Replace all nonvalid hexadecimal characters with 0’s:
chucknorris becomes c00c0000000
Pad out to the next total number of characters divisible by 3 (11 → 12):
c00c 0000 0000
Split into three equal groups, with each component representing the corresponding colour component of an RGB colour:
RGB (c00c, 0000, 0000)
Truncate each of the arguments from the right down to two characters.
Which, finally, gives the following result:
RGB (c0, 00, 00) = #C00000 or RGB(192, 0, 0)
Here’s an example demonstrating the bgcolor attribute in action, to produce this “amazing” colour swatch:
<table>
<tr>
<td bgcolor="chucknorris" cellpadding="8" width="100" align="center">chuck norris</td>
<td bgcolor="mrt" cellpadding="8" width="100" align="center" style="color:#ffffff">Mr T</td>
<td bgcolor="ninjaturtle" cellpadding="8" width="100" align="center" style="color:#ffffff">ninjaturtle</td>
</tr>
<tr>
<td bgcolor="sick" cellpadding="8" width="100" align="center">sick</td>
<td bgcolor="crap" cellpadding="8" width="100" align="center">crap</td>
<td bgcolor="grass" cellpadding="8" width="100" align="center">grass</td>
</tr>
</table>
This also answers the other part of the question: Why does bgcolor="chucknorr" produce a yellow colour? Well, if we apply the rules, the string is:
c00c00000 => c00 c00 000 => c0 c0 00 [RGB(192, 192, 0)]
Which gives a light yellow gold colour. As the string starts off as 9 characters, we keep the second ‘C’ this time around, hence it ends up in the final colour value.
I originally encountered this when someone pointed out that you could do color="crap" and, well, it comes out brown.
Best Answer
As the "outside" name suggests, the numbers are placed outside the element so you cannot affect them with li's background color. A workaround for this may be using an additional div inside the li:
Then add the following CSS for the div:
This will move the div to appear under the number (that's the -20px value) and the text in it back to the right place (that 20px value).