> For the complete documentation index, see [llms.txt](https://petercheng7788.gitbook.io/developer-note/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://petercheng7788.gitbook.io/developer-note/frontend/css.md).

# CSS

## Chain of css syntax

```css
// single class with multiple conditions
div.test {
    background-color: yellow;
}
.flex-container >div.red1{
    background-color: red;
}
.red1.red2{
    background-color: red;
}

// multiple class share same css
.red1,.red2 {
     background-color: red;
}
```

## CSS Specificity

* The final css result is due to total mark of css, style with higher marks win
* CSS mark counting can be separated into different slot

### Element Selector (Slot 1)

<figure><img src="/files/fJLY93cuSb4g4uXfzz2V" alt=""><figcaption></figcaption></figure>

### Class Selector (Slot 2)

<figure><img src="/files/wUxa6Bgu9qStmsA37TVx" alt=""><figcaption></figcaption></figure>

<figure><img src="/files/n6JOIKvKONopAmYww1qx" alt=""><figcaption></figcaption></figure>

### ID Selector (Slot 3)

<figure><img src="/files/WnqZOwy3D7ghCn8wggTT" alt=""><figcaption></figcaption></figure>

### Inline Style (Slot 4)

<figure><img src="/files/MF09enc9iS3DWDt3jmXH" alt=""><figcaption></figcaption></figure>

## BEM Naming

`{block}_{element}--{modifer}`

[`https://getbem.com/naming/`](https://getbem.com/naming/)

## CSS Module

* CSS Modules locally scope CSS by automatically creating a unique class name. This allows you to use the same class name in different files without worrying about collisions

## Pre-processor

* It is a tool or programming language that extends the capabilities of CSS (Cascading Style Sheets) by introducing additional features, e.g: sass
* the code is compiled into regular CSS that can be used by web browsers. This compilation process typically involves running a preprocessor-specific command or using a build tool like webpack or gulp.

## Post CSS

* PostCSS is not a preprocessor, but a post-processor. That means it does not have its own syntax, but instead uses standard CSS and modifies it with javascript plugin
* Then it compile to pure css which is same as pre-processor

<figure><img src="/files/j0da7v55sZJKztOOm3nn" alt=""><figcaption></figcaption></figure>

* The processor will compile through the plugin that defined in the file

```bash
npm install autoprefixer postcss postcss-cli
```

{% code title="postcss.config.js" %}

```javascript
module.exports = {
  plugins: {
    autoprefixer: {},
  }
}
```

{% endcode %}

* Compile

```
npx postcss styles.css -o dist/styles.css
```


---

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