CSS變量通過存儲(chǔ)可重用值并實(shí)現(xiàn)一處修改多處生效，提升了代碼的整潔性與維護(hù)性。其核心作用是簡(jiǎn)化樣式表管理，支持動(dòng)態(tài)更新和局部作用域控制。使用時(shí)需以--前綴定義變量，通過var()函數(shù)調(diào)用，并注意命名規(guī)范與作用域劃分，同時(shí)警惕拼寫錯(cuò)誤及兼容性問題。具體要點(diǎn)如下：1. 使用--prefix定義變量，通常在:root中聲明全局變量；2. 通過var()函數(shù)引用變量；3. 可存儲(chǔ)顏色、尺寸、陰影等任意CSS值；4. 局部變量應(yīng)定義在特定選擇器內(nèi)以避免沖突；5. 動(dòng)態(tài)更新可通過JavaScript或媒體查詢實(shí)現(xiàn)；6. 注意拼寫檢查、繼承行為及瀏覽器兼容性問題。合理使用CSS變量能顯著提升開發(fā)效率與代碼可維護(hù)性。

Using CSS variables (also known as custom properties) can make your stylesheets cleaner, more maintainable, and easier to update. They let you store reusable values—like colors, font sizes, spacing—and change them in one place instead of hunting through your code.

What Are CSS Variables?

CSS variables are defined using the -- prefix inside a selector, usually :root for global scope. You access them with the var() function.

:root {
  --primary-color: #007bff;
  --spacing: 1rem;
}

Then use them like this:

.button {
  background-color: var(--primary-color);
  padding: var(--spacing);
}

They’re not just for colors—you can store anything: sizes, shadows, font stacks, even complex gradients.

How to Scope Variables Locally

By default, defining variables on :root makes them globally available. But sometimes you want variables that only apply in certain parts of the site—like a dark theme or a specific component.

Just define them on a selector:

.card {
  --bg-color: #f8f8f8;
  background-color: var(--bg-color);
}

Now, only elements under .card will see that value. This helps avoid naming conflicts and keeps things modular.

Tips:

• Use meaningful names (--header-padding, not --p1)
• Keep local variables tightly scoped
• Don’t overdo it—some values are fine being hard-coded

Updating Variables Dynamically

One of the big wins with CSS variables is being able to change them at runtime—say, switching themes or adjusting layout based on user input.

You can do this in JavaScript:

document.documentElement.style.setProperty('--primary-color', '#ff0000');

Or with media queries:

@media (max-width: 600px) {
  :root {
    --spacing: 0.5rem;
  }
}

This flexibility makes responsive design and theming easier without needing extra classes or preprocessors.

Common Pitfalls and Gotchas

Even though CSS variables are powerful, there are a few things to watch out for:

• No fallback if misspelled: If you typo a variable name, like var(--primry-color), it won’t work and won’t warn you.
• Cascading behavior matters: Variables inherit like normal properties, so changing a parent’s variable affects children.
• Older browser support: Most modern browsers support them, but not IE11.

To stay safe:

• Double-check variable names
• Use fallbacks when needed: color: var(--text-color, black);
• Consider tools like PostCSS if you need broader compatibility

That’s the core of working with CSS variables. They’re not complicated, but they do require attention to naming and scope. Once you get used to them, you’ll probably wonder how you ever managed without.

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