Discuss the possible reasons why modifying css in php projects is invalid

In web development, PHP, as a popular back-end development language, is often used to process client requests and output dynamic pages or APIs. During the page rendering process, HTML, CSS, and JavaScript constitute the core technology stack of the front-end, and their combination determines the final display effect of the page. Sometimes, we modify the CSS in the PHP project, but find that the modified effect does not take effect. This is the topic to be discussed in this article.

1. How to load CSS

In web development, there are many ways to load CSS, the most common of which are the following two:

• Inline style: Write the style directly in the style attribute of the HTML element, as shown below:

  <div style="color: red;">Hello, world!</div>

  Inline style has the highest weight and priority, and will override other styles.

• External style sheet: defined in a separate CSS file, introduced through the <link> tag, as follows:

  <link rel="stylesheet" href="style.css">

  External style sheets have lower weight than inline styles, but usually have the highest priority, overriding inline and embedded styles.

In PHP projects, due to the dynamic nature of web applications, external style sheets are usually used to manage CSS, which also facilitates front-end and back-end separation and code management. However, if we don’t understand the priority of CSS loading, we may encounter situations where modifying CSS has no effect.

2. Priority and cascading rules

Why does modifying CSS have no effect? This is due to CSS style precedence and cascading rules. In CSS, the priority of styles is calculated based on the source and type of the style to determine the final style that takes effect. The priority order of CSS styles is as follows:

1. !important Declared style;
2. Inline style;
3. id selector;
4. Class selector, attribute selector, pseudo-class selector;
5. Element selector, pseudo-element selector;
6. Wildcard selector, sub-selector, adjacent selector , universal sibling selector.

In this priority order, the more specific the selector and the higher the priority, the easier it is for the corresponding style to take effect.

In addition, CSS style cascading rules will also affect the final effect of the style. Cascading rules compare styles from different sources according to priority and specificity, and merge them according to certain rules. Its priority and type are as follows:

1. Importance: !important has the highest priority and is not affected by other rules;
2. Speciality: The higher the selector's specificity value, the higher the priority;
3. Order: For styles from the same source, styles defined later have higher priority and can override previously defined styles;
4. Inheritance: Child elements inherit the style of the parent element, but there are parsing issues such as escaping the small equal and large equal signs.

3. Debugging and modification of CSS code

Understanding CSS style priority and cascading rules, we can use the correct method to debug and modify CSS code in PHP projects. CSS modifications. Specifically, you can use the following methods:

3.1 Clear the browser cache

In browsers, the caching mechanism is often used to increase the speed of page loading. If the CSS file is modified but the browser still uses the cached styles, then our style modifications will not take effect. Therefore, we need to clear the browser cache and reload the page to ensure the latest styles are used.

3.2 Use developer tools to view styles

The browser’s developer tools are one of our key tools for debugging CSS styles. In the developer tools, we can view the styles used by the current element and the applied style source to determine why the style modification is invalid. In the Chrome browser, we can open the developer tools through the following steps:

1. Click the three vertical dots in the upper right corner of the browser window and select More tools -> Developer Tools;
2. Or press the shortcut key Ctrl Shift I.

In the developer tools, we can use the Elements tag to view the HTML element structure of the current page, and the Styles tag to view the applied styles of elements and the source of the styles.

3.3 Use high-priority selectors

If the priority of the style is not enough to override the existing style, we can use a high-priority selector. For example, using a style declared with !important can override any other style; using an id selector, you can increase the priority of the style to ensure that the style takes effect.

3.4 Undo cascading rules

If the style is affected by some cascading rules, we can use the selector to increase the specificity or adjust the position of the style to undo the cascading The impact of rules. For example, using a more specific selector, a higher priority selector, or a later style definition can change the style cascading rules.

4. Conclusion

The problem of invalid CSS style modification in PHP projects is often caused by a lack of understanding of the priority and cascading rules of CSS styles. By debugging methods such as clearing the browser cache, using developer tools to view styles, using high-priority selectors, and undoing cascading rules, we can solve the problem of invalid style modifications and ensure that the web application runs properly and interacts with users.

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