What does css3 grammar rules consist of?

css3 grammar rules consist of three parts: "selector", "attribute" and "attribute value". "Selector" specifies the object to be targeted by CSS style coding, "property" is the set style option provided by CSS, and "property value" is a parameter used to display the effect of the property.

The operating environment of this tutorial: Windows 7 system, CSS3&&HTML5 version, Dell G3 computer.

Style is the smallest syntax unit of CSS. CSS syntax consists of three parts: selector, attribute and attribute value.

• Selector

  Specify the object to be targeted by this set of style coding, which can be an XHTML tag or It is a tag of a specific id or class (preceded by #);

• Attribute (Property)

  attribute is the core of CSS style control, and is used in every XHTML Both labels and CSS provide rich style attributes, such as color, size, positioning, floating method, etc.

  Attributes are set style options provided by CSS. The attribute name consists of one or more words, and multiple words are connected by hyphens. This can intuitively represent the effect of the attribute to be styled.
  

• Attribute value (value)

  refers to the value of the attribute, which is a parameter used to display the effect of the attribute. It includes numerical values ​​and units, or keywords.

Different writing methods and units of values

In addition to the English word red, we can also use hexadecimal Color value #ff0000:

p { color: #ff0000; }

In order to save bytes, we can use the CSS abbreviation:

p { color: #f00; }

We can also use RGB values ​​in two ways:

p { color: rgb(255,0,0); }
p { color: rgb(100%,0%,0%); }

Note that when using RGB percentages, the percent sign is written even when the value is 0. But in other cases there is no need to do this. For example, when the size is 0 pixels, there is no need to use px units after 0, because 0 is 0, no matter what the unit is.

Remember to write quotation marks

Tip: If the value is several words, add quotation marks to the value:

p {font-family: "sans serif";}

CSS Advanced syntax: Grouping selectors

You can group selectors so that grouped selectors share the same declaration.

Use commas to separate the selectors that need to be grouped. In the example below, we have grouped all heading elements. All title elements are green.

h1,h2,h2,h3,h5,h6 {
color: green;
}

(Learning video sharing: css video tutorial)

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