Summary of usage of background-position attribute in css

backgroundThe property is one of the most common properties in CSS. To implement CSS cutout, you only need to use one property: background-position. Background-position is used to control the position of the element's background image. The trick is that you actually specify the position of the upper left corner of the image relative to the upper left corner of the element. It accepts three values: Keywords, such as top, right, bottom, left and center; Length values, such as px, em, rem, etc.; hundred Score%. The following content will talk about the usage of background-position attribute.

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background-position property usage

1.

css background-position property

The background-position property sets the starting position of the background image.

This property sets the position of the original background image (defined by background-image). If the background image is to be repeated, it will start from this point.

Tip: You need to set the background-attachment property to "fixed" to ensure that this property works properly in Firefox and Opera.

2.

Background-position percentage principle

For background-size:100% auto, it means that the width of the background image is the element width * 100%, and the height is scaled proportionally . See css3 background for details.

It is natural to think that the percentage of background-position is calculated based on the width of the parent element, but background-position is really not. It has its own set of principles.

3.

The use of background-position in CSS

The first one of the two values ​​​​is horizontal positioning, which we call x-axis positioning. The latter value is the longitudinal positioning, which we call the y-axis positioning.

If there is only one value, the default is the x-axis direction. At this time, the y-axis direction defaults to aligning up and down, which is center.

4.

css uses the background-position attribute to complete the code of the sprite image.

The sprite image is CSS Sprite, and some people call it CSS sprite. A CSS image merging technology is to merge multiple small icons into one image, and then use CSS background-position to display the part that needs to be displayed.

It can reduce the number of requests to the server when loading web page images, improve the loading speed of the page, and solve the problem of flashing white when the mouse slides over IE6.

5.

The background-position you don’t know about the background series

We know that background-position is used to specify the offset value of the background image, which can make a The picture starts from a specific position. CSS Sprites achieves the expectation of merging HTTP requests by splicing multiple small images into one large image, and then using background-position to specify the area that needs to be displayed.

Related Questions and Answers

1. background-position There will be a border that cannot be removed after capturing the image

2.The use of background-position is confusing.

3. Questions about the percentage of background-position?

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