what are css units

CSS units are standardized values used to measure and describe the size, distance and other properties of elements. They are used to specify the size, position, spacing, font size, etc. of elements. CSS units can be divided into absolute units and relative units. There are two categories of units. Absolute units are suitable for fixed-size elements and typographic style definitions, while relative units are suitable for responsive layouts and mobile device development. By rationally selecting and combining these units, flexible layout and size definition can be achieved, providing a good user experience.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

CSS units are standardized values used to measure and describe element dimensions, distances, and other properties. They are used to specify the size, position, spacing, font size, etc. of an element. CSS units can be divided into two categories: absolute units and relative units.

1. Absolute unit:

- Pixel (px): Pixel is the most commonly used absolute unit, representing a physical pixel on the screen. Pixel is a relatively fixed unit and may correspond to different physical sizes on different devices.

- Inch (in): Inch is the international standard unit, 1 inch is equal to 2.54 centimeters.

- Centimeter (cm): Centimeter is the international standard unit, 1 centimeter is equal to 10 millimeters.

- Millimeter (mm): Millimeter is the international standard unit, 1 millimeter is equal to 0.1 centimeter.

- Point (pt): Point is a unit commonly used in the printing industry. 1 point is equal to 1/72 inch.

- Double printing point (pc): Double printing point is a commonly used unit in the printing industry, 1pc is equal to 12 points.

2. Relative unit:

- Percent (%): The percentage unit is calculated relative to the size of the parent element. For example, if an element's width is set to 50%, its width will be half the width of its parent element.

- em (em): The em unit is calculated relative to the font size of the element. For example, if an element's font size is set to 2em, then its dimensions will be twice the font size of the parent element.

- rem (rem): The rem unit is calculated relative to the font size of the root element (that is, the html element). Unlike em, the calculation of rem units is not affected by the font size of the parent element.

- Viewport width (vw): The vw unit represents the percentage of the viewport width. The viewport refers to the visible area of the browser window or device screen. For example, if an element's width is set to 50vw, then its width will be half the width of the viewport.

- Viewport height (vh): The vh unit represents the percentage of the viewport height. For example, if an element's height is set to 50vh, then its height will be half the viewport height.

- Viewport minimum size (vmin): The vmin unit represents the percentage of the smaller of the viewport width and the viewport height. For example, if an element's height is set to 50vmin, its height will be half the smaller of the viewport width or the viewport height.

- Maximum viewport size (vmax): The vmax unit represents the percentage of the larger of the viewport width and viewport height.

The choice of CSS units depends on specific needs and design requirements. Absolute units are suitable for fixed-size elements and typographic style definitions, while relative units are suitable for responsive layouts and mobile device development. By rationally selecting and combining these units, flexible layout and size definition can be achieved, providing a good user experience. In addition, you also need to pay attention to the conversion and compatibility between different units to avoid dimensional confusion or abnormal display.

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