Because style table items are composed of attributes and their values, it is necessary to understand the various units of the attribute values. In CSS, different units are different from those in HTML.
1. Length unit
Unit Type description
Cm
Width of m letters in em EMS current font
The x letter height in the current font of the ex exs.
In inch
Mm
Pc Picas 1 pica = 12
Pt point 1 = 1/72 inch
Pixel display unit
Note: not all browsers support the above length units. For example, IE3.x does not support em and ex. NS4.0 does not support pc units.
In the above unit, you must specify em and ex.
The height represented by "em" is the height of the capital letter "M" (or "H"). If the current font is 12, then em is 12. Generally, the default font of the browser is 12. If the default font size is changed, the em value is adjusted accordingly.
For example, if the font size in the <H1> mark is set to 1.5em, the browser will execute the following process during HTML compilation:
(1) Read the default font size value, such as number 12;
(2) read the relative definition value 1.5em;
(3) display the 18 font (12pt X 1.5 = 18pt ).
It can be seen that the em unit is defined based on the default value of the user's browser, so that both the web designer and the viewer have control over the font size-the designer can specify the need to expand (or contract) the actual display size is selected by the user.
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