字体CSS速记需要字体大小吗？

Question

我想用fontCSS缩写包括所有字体属性(如font-style,font-weight,font-size,等).

如果我使用所有属性,它都有效.

p.ex1 {
    font: 15px arial, sans-serif;
}

p.ex2 {
    font: italic bold 12px/30px Georgia, serif;
}

<p class="ex1">This is a paragraph. This is a paragraph. This is a paragraph. This is a paragraph. This is a paragraph. This is a paragraph. This is a paragraph. This is a paragraph.</p>
<p class="ex2">This is a paragraph. This is a paragraph. This is a paragraph. This is a paragraph. This is a paragraph. This is a paragraph. This is a paragraph. This is a paragraph.</p>

但是,当我只有font-weight和font-family,它没有.

p.ex1 {
    font: 900 Georgia, serif;
 }

<p class="ex1">This is a paragraph. This is a paragraph. This is a paragraph. This is a paragraph. This is a paragraph. This is a paragraph. This is a paragraph. This is a paragraph.</p>

为什么？是否有必要指定font-size何时使用fontCSS速记？

Answer 1

是.

来自:developer.mozilla.org/[ ....]/font

注意:使用CSS字体速记时有一些注意事项.
如果不满足这些条件,则该属性无效并完全被忽略.

• 除了使用关键字时,必须定义font-size和font-family属性的值.
• 并非所有font-variant值都允许.
• 只允许CSS 2.1中定义的值,即普通和小型上限.
• 虽然不能通过字体直接设置,但font-stretch,font-size-adjust和font-kerning的值也会重置为其初始值.
• 值的顺序不是完全免费的:必须在font-size值之前定义font-style,font-variant和font-weight(如果有).
  必须在font-size之后立即定义行高值,前面是强制/.
• 最后,font-family是必需的,必须是最后定义的值(继承值不起作用).