fonts - font: .81em/150% Arial; why is it 0.81?

Question

I saw this font declaration on a web page and I don't understand what it does. I googled, but no results. Any idea?

font: .81em/150% Arial, Helvetica, sans-serif;

I know what the Arial, Helvetic, sans-serif part of it does; I'm wondering what the .81em does.

why is it 0.81? why not it is 0.8 or 0.82 or other value?

Answer 1

这是一次定义字体大小和行高的简写。

0.81 可能是随机的，只是适合的尝试

Answer 2

可能有人想将 font-size 设置为 13px 并使用一些转换工具来转换 em，然后发现，例如这个表有 .813em 为 13px，然后向下舍入。