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In this article Xiaobian for you to introduce in detail "how to use value replication in HTML", the content is detailed, the steps are clear, the details are handled properly, I hope this "how to use value replication in HTML" article can help you solve your doubts, the following follow the editor's ideas slowly in-depth, together to learn new knowledge.

Unintentionally, we will enter some repeated values:

P {margin: 0.5em 1em 0.5em 1em;}

With value copying, you can type this pair of numbers frequently. The above delineation is equivalent to the following delineation rules:

P {margin: 0.5em 1em;}

These two values are about 4 in the back. How is this done? CSS defines rules that allow you to specify less than 4 values for the outer margin. The rules are as follows:

If the value of the left margin is missing, the value of the right margin is used.

If the value of the bottom margin is missing, the value of the top margin is used.

If the value of the right margin is shorter, the value of the upper margin is used.

The following figure provides a more intuitive way to appreciate this:

In other words, if three values are specified for the outer margin, the fourth value (that is, the left margin) is copied and lost from the second value (the right margin). If two values are given, the fourth value is copied from the second value, and the third value (bottom margin) is copied from the first value (top margin). At the end of a case, if only one value is given, then the other three outer margins will be copied and lost by this value (upper outer margin).

To control this easy mechanism, you only need to specify important values instead of applying four values to everything, for example:

H2 {margin: 0.25em 1em 0.5em;} / * equivalent to 0.25em 1em 0.5em 1em * / h3 {margin: 0.5em 1em;} / * equivalent to 0.5em 1em 0.5em 1em * / p {margin: 1px;} / * equivalent to 1px 1px 1px 1px * /

This method has a small harm, and you are bound to encounter this problem in the end. If you wish to set the upper and left margins of the p element to 20 pixels, and the lower and right margins to 30 pixels. In this environment, you must write:

P {margin: 20px 30px 30px 20px;} read here, this article "how to use value replication in HTML" has been introduced. If you want to master the knowledge of this article, you still need to practice and use it to understand it. If you want to know more about related articles, welcome to follow the industry information channel.

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