Thoroughly understand the difference between unit px and Em,rem in CSS

2016-03-11 17:32 Most of the domestic front-end likes to use PX, and the foreign sites mostly like with Em and REM, then what is the difference between the three, and what are the pros and cons of each? PX Features: 1. IE cannot adjust the font size of those using PX as unit; 2. Most of the foreign sites can be adjusted because they use the EM or REM as font units; 3. Firefox can adjust PX and em,rem, and the lower version of IE (or kernel) is not supported. px Pixels (Pixel). Relative length units. Pixel px is relative to the screen resolution of the monitor.? em is the relative length unit. The font size relative to the text within the current object. If the font size of the current inline text is not artificially set, the default font size is relative to the browser. The default font height for any browser is 16px. All non-adjustable browsers are compliant with: 1EM=16PX. So 12px=0.75em,10px=0.625em. To simplify the conversion of font-size, you need to declare font-size=62.5% in the body selector in the CSS, which makes the EM value 16px*62.5%=10px, so 12px=1.2em, 10px=1em, That means you just have to divide your original PX value by 10 and then put EM in as the unit. EM features: 1. The value of EM is not fixed; 2. EM inherits the font size of the parent element. So when we write CSS, we need to pay attention to two points: 1. The body selector declares font-size=62.5%;2. Divide your original PX value by 10 and then replace it with EM as Unit 3. Recalculate the EM values of those magnified fonts. Avoid duplicate declarations of font size. This is to avoid the 1.2 * 1.2 = 1.44 phenomenon. For example, when you declare a font size of 1.2em in #content, you can only have 1em when declaring the font size of p, not 1.2em, because this em is not em, it becomes 1em=12px because it inherits the font height of #content. REM Features: REM is a new relative unit of CSS3 (root em, root em), and this unit has aroused widespread concern. What is the difference between this unit and EM? The difference is that when you use REM to set the font size for an element, it is still relative size, but relative to the HTML root element. This unit is a combination of relative size and absolute size of the advantages in one, through it can only modify the root elements in proportion to adjust all font size, but also to avoid the size of the font-layer composite chain reaction. Currently, in addition to IE8 and earlier versions, all browsers support REM. For browsers that do not support it, the workaround is simple enough to write an absolute unit statement. These browsers will ignore the use of RThe font size set by EM. Here is an example: p {font-size:14px; font-size:.875rem;} Summary 1, the browser's default font size is 16px2, if the element itself is not set the font size, then all the property values on the element itself such as "boder, width, height, padding, margin, line-height" equivalent, We can all calculate the 1÷ parent element's Font-sizex need to convert the pixel value by the following formula = EM value then the element sets the font size, other properties of this element, such as "border, width, height, padding, margin, Line-height "calculation needs to be calculated according to the following formula: The 1÷ element's own Font-sizex need to convert the pixel value = em value note:? What font units you choose to use are primarily determined by your project, and if your user base is using the latest version of the browser, it is recommended to use REM, If you want to consider compatibility, use PX, or both.

Thoroughly understand the difference between units px and Em,rem in CSS