(1 / parent font-size) x required pixel value = em value
（1 / 父字体大小） x 所需的像素值 = em 值
Make it so your fonts are readable, but not obscenely large, and make the font-size indicate the importance of the information.
保持文字的可读性，但不要太大，让字体的大小表现信息的重要性。
The “Log in”-link (hint: in the yellow box) should have a greater font-size — also icons would do the job.
这个“Log-in”链接（提示：在黄色色块中）字体应该更大些，或者用图标链接代替小的文字链接。

权威例句

That button also lets you buy the book (in the case of a sample), skip to a specific page, bookmark, look up a word in the including Collins dictionary, view the book's table of contents, and adjust the font size -- there are eight font sizes in all.
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One programmer has taken it upon himself to provide a fix for the change to bring the font size back to less-squinting normal.
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Customers can touch to look up words, highlight passages and customize their reading experience by adjusting the font size and style, and experience lightning-fast page turns by swiping or using the device's contoured physical buttons.
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font size