负数

Baseline 2023

Newly available

Since September 2023, this feature works across the latest devices and browser versions. This feature might not work in older devices or browsers.

The negative descriptor of the @counter-style at-rule lets you define how negative counter values are represented when defining custom counter styles. The value of the negative descriptor defines the symbols to be added before and after the counter representation when the counter's value is negative.

语法

css
/* One <symbol> value */
negative: "--"; /* Adds '--' before if counter value is negative */

/* Two <symbol> values */
negative: "(" ")"; /* Adds '(- before and ')' after if counter value is negative */

Values

The negative descriptor accepts up to two <symbol> values.

<symbol>

If only one value is specified, it is added before the counter representation when the counter is negative. If two values are specified, the first one is added before and the second one is added after the counter representation when the counter is negative.

描述

If the counter value is negative, the specified <symbol> for the negative descriptor is added before the counter representation, replacing the default - for negative values. The second <symbol>, if specified, is added after the counter representation.

The negative descriptor is relevant in two cases: if counter styles have the system value of symbolic, alphabetic, numeric, and additive and the count is negative; and if system value is extends and the extended counter style itself uses a negative sign. For systems that don't support negative counter values, specifying the negative descriptor has no effect and is ignored.

正式定义

Related at-rule@counter-style
Initial value"-" hyphen-minus
Computed valueas specified

正式语法

negative = 
  <symbol> <symbol>?  

<symbol> = 
  <string>        |
  <image>         |
  <custom-ident>  

<image> = 
  <url>       |
  <gradient>  

<url> = 
  <url()>  |
  <src()>  

<url()> = 
  url( <string> <url-modifier>* )  |
  <url-token>                      

<src()> = 
  src( <string> <url-modifier>* )

示例

Rendering negative counters

此示例 扩展 了 decimal 列表样式。negative 描述符用于在负计数器值之前和之后添加 (- 和 )。

HTML

html
<ol start="-3">
  <li>Negative three</li>
  <li>Negative two</li>
  <li>Negative one</li>
  <li>Zero</li>
  <li>One</li>
</ol>

CSS

css
@counter-style neg {
  system: extends decimal;
  negative: "(-" ")";
  suffix: ": ";
}

ol {
  list-style: neg;
}

结果

当计数器值小于零时，才会在标记符中添加 negative 描述符值中列出的前缀和后缀。

规范

规范
CSS 计数器样式级别 3
# counter-style-system

浏览器兼容性

BCD 表格仅在浏览器中加载

另请参见