CSS precedence
CSS Order of Style
In web development, the order of CSS style sheets plays an important role in the display effect of the page. Correct CSS precedence ensures that styles are applied as intended and avoids unnecessary conflicts and overrides. This article will detail the principles and impacts of CSS precedence.
Inline Styles
Inline styles are styles written within HTML tags. They have the highest priority and override styles in external and internal style sheets.
Sample code:
<div style="color: red;">This is inline style text</div>
External Style Sheet
An external style sheet introduces styles by linking to an external CSS file and placing it in the head section of an HTML document.
Sample code:
<head>
<link rel="stylesheet" href="styles.css">
</head>
Internal Style Sheet
An internal style sheet is a style sheet written in the style tag in the head of an HTML document. Its priority is lower than inline styles, but higher than external style sheets.
Sample Code:
<head>
<style>
.title {
font-weight: bold;
}
</style>
</head>
Selector Specificity
In CSS, the specificity of different selectors also affects the order in which styles are applied. Generally speaking, the specificity, from highest to lowest, is: inline style > ID selector > class selector > tag selector.
Sample code:
.title {
color: red;
}
#main-title {
color: blue;
}
<div class="title" id="main-title">This is a title</div>
In the example above, the title text will be blue because the ID selector has higher precedence than the class selector.
Style Inheritance
Certain properties are inherited by child elements, meaning that the parent element’s styles are automatically applied to the child elements.
Sample code:
.container {
font-family: Arial, sans-serif;
}
<div class="container">
<p>This is a paragraph</p>
</div>
In the example above, the paragraph will inherit the font style of .container.
!important Rule
In CSS, the !important rule can override other styles and enforce certain styles on an element. However, overuse of !important should be avoided, as it can make style maintenance difficult.
Sample Code:
.title {
color: red !important;
}
<div class="title" style="color: blue;">This is a title</div>
In the example above, the title text will be red because the !important rule has the highest precedence.
CSS Cascading Order
When different styles conflict, CSS uses specific rules to determine the final style.
- Importance (!important): Styles defined by the !important rule override all other styles.
- Source Order: Styles defined later in the style sheet override earlier styles.
- Selector Specificity: The specificity of the selector determines the priority of a style. More specific styles override less specific styles.
- Inheritance: Some properties are inherited; child elements inherit properties from their parent.
Conclusion
Correctly understanding and mastering the order of CSS styles is crucial for web development. Properly writing CSS style sheets and applying style priorities correctly can ensure the desired page display and reduce unnecessary conflicts and overrides.