Difference between EM (times) and PX

Chinese websites, including the three major portals, as well as the blue ideal that leads the Design Trend of Chinese websites, and chinaui all use PX as the font unit. Only Baidu has an adjustable table rate. On the other side of the ocean, almost all mainstream sites use EM as the font unit, that is, adjustable. True, PX is easier to use than em. Most readers do not know why Em is or how much PX It is equivalent. Foreign people pay so much attention to the ease-of-use of websites (accessibility), not only because of itsHumanistic SpiritThe direct cause may be that there is a law to constrain them-for example, the United StatesSection 508To make websites easy to use.

Key Points:1. ie cannot adjust the font size that uses PX as the unit;
2. The reason why most foreign websites can be adjusted is that they use EM as the font unit;
3. Firefox can adjust PX and Em, but more than 96% of Chinese users use IE browser (or kernel ).
　　Pixel (pixel ). The unit of relative length. Pixel PX is relative to the screen resolution of the monitor.
　　Em is the unit of relative length. The font size relative to the text in the current object. If the font size of the text in the row is not set manually, the default font size is relative to that of the browser.
The default font height of any browser is 16 PX. All unadjusted browsers match: 1em = 16px. Then 12px = 0.75em, 10px = 0.625em. To simplify font-size conversion, you must declare font-size = 62.5% in the body selector in CSS, which changes the EM value to 16px * 62.5% = 10px, so that 12px = 1.2em, 10px = 1em, that is, you only need to divide your original PX value by 10, and then change to Em as the unit.
　　Em has the following features:
1. The EM value is not fixed;
2. Em inherits the font size of the parent element.
　　Therefore, when writing CSS, pay attention to the following two points:
1. Declare font-size = 62.5% in the body selector;
2. Divide your original PX value by 10 and change it to Em as the unit;
3. recalculate the EM values of the enlarged fonts. Avoid repeated statement of font size.
That is, to avoid 1.2*1.2 = 1.44. For example, if you declare in # content that the font size is 1.2em, the font size of P can only be 1em, not 1.2em, because this EM is not em, it becomes 1em = 12px because it inherits the font of # content.
Except for the 12 PX Chinese character, the 12 PX (1.2em) Chinese Character obtained by the above method is not equal to the font size defined by 12 PX directly in IE, but a little larger. This problem has been solved by jorux. You only need to replace 62.5% with 63% in the body selector to display it normally. The reason may be that when ie processes Chinese characters, the floating point value accuracy is limited. I don't know if there are any other explanations.

Difference between EM (times) and PX