max()

max() 方法接受一个或多个用逗号分隔的表达式作为他的参数，数值最大的表达式的值将会作为指定的属性的值。

表达式可以是数学运算 (可在 calc() 了解更多信息), 直接数值，或者是其他表达式，例如 attr()，这将会计算成一个合法的参数类型（例如 <length>），也可以是嵌套的 min() 和 max() 函数。

你可以使用你的表达式中分别使用不同的单位。需要时，你也可以使用小括号来设定运算顺序。

• Math expressions involving percentages for widths and heights on table columns, table column groups, table rows, table row groups, and table cells in both auto and fixed layout tables may be treated as if auto had been specified.
• It is permitted to nest min() and other max() functions as expression values. The expressions are full math expressions, so you can use direct addition, subtraction, multiplication and division without using the calc() function itself.
• The expression can be values combining the addition ( + ), subtraction ( - ), multiplication ( * ) and division ( / ) operators, using standard operator precedence rules. Make sure to put a space on each side of the + and - operands. The operands in the expression may be any <length> syntax value.
• Oftentimes you will want to combine min() and max() values, or use max() within a clamp() or calc() function.

<max()> = 
  max( <calc-sum># )  

<calc-sum> = 
  <calc-product> [ [ '+' | '-' ] <calc-product> ]*  

<calc-product> = 
  <calc-value> [ [ '*' | '/' ] <calc-value> ]*  

<calc-value> = 
  <number>        |
  <dimension>     |
  <percentage>    |
  <calc-keyword>  |
  ( <calc-sum> )  

<calc-keyword> = 
  e          |
  pi         |
  infinity   |
  -infinity  |
  NaN        

Another use case for CSS functions is allow a font size to grow while ensuring it is at least a mimum size, enabling responsive font sizes while ensuring legibility.

Let's look at some CSS:

h1 {
  font-size: 2rem;
}
h1.responsive {
  font-size: max(4vw, 2em, 2rem);
}

The font-size will at minimum be 2rems, or twice the default size of font for the page. This ensure it is legible and ensures accessibility

<h1>This text is always legible, but doesn't change size</h1>
<h1 class="responsive">
  This text is always legible, and is responsive, to a point
</h1>

Think of the max() function as finding the minimum value allowed for a property.

When max() is used for controlling text size, make sure the text is always large enough to read. A suggestion is to use the min() function nested within a max() that has as its second value a relative length unit that is always large enough to read. For example:

small {
  font-size: max(min(0.5vw, 0.5em), 1rem);
}

This ensures a minimum size of 1rem, with a text size that scales if the page is zoomed.

• calc()
• clamp()
• min()
• CSS Values