1.ID選擇器用于唯一元素，類(lèi)選擇器用于多個(gè)元素。2.ID具有更高優(yōu)先級(jí)且不可重復(fù)，適用于獨(dú)特元素如導(dǎo)航欄或錨點(diǎn)鏈接；類(lèi)選擇器更靈活可復(fù)用，適合多處應(yīng)用相同樣式及模塊化組件。3.開(kāi)發(fā)者有時(shí)避免使用ID因高特異性可能引發(fā)樣式覆蓋問(wèn)題，但其在JavaScript和URL片段中仍有用途。

The main difference between a class selector and an ID selector in CSS is how they are used to target HTML elements. An ID selector targets one unique element on the page, while a class selector can be applied to multiple elements.

ID Selector Targets One Unique Element

An ID is meant to be unique within a page. That means you should only have one element with a specific ID at a time. You use the # symbol followed by the ID name in your CSS to style that single element.

For example:

#header {
  background-color: #333;
  color: white;
}

In this case, only the element with id="header" will get that styling. If you accidentally use the same ID more than once, it won’t break your site visually (usually), but it’s invalid HTML and can cause issues with JavaScript or accessibility tools.

Also, because IDs are unique, they have higher specificity in CSS. That means styles applied via an ID are harder to override unless you write even more specific rules — something that can lead to messy code if overused.

Class Selector Applies to Multiple Elements

A class, on the other hand, can be used on as many elements as you like. It’s perfect when you want to apply the same style to different parts of your page. In CSS, you target classes using a dot (.) followed by the class name.

Like this:

.highlight {
  background-color: yellow;
}

Now, any element with class="highlight" will get that yellow background. You can combine classes too — just separate them with spaces in the HTML:

<p class="highlight important">This is important text.</p>

Here, both .highlight and .important styles will apply to the paragraph.

Classes are more flexible and reusable, making them the go-to choice for most styling tasks. They also play nicely with frameworks like Bootstrap or Tailwind, where utility classes are heavily used.

When to Use ID vs Class

• ? Use an ID when:

  • You're styling a single, unique element (like a main navigation bar or hero section).
  • You need to jump to a specific part of the page with anchor links.
  • You're working with JavaScript and need a reliable way to access one particular element.

• ? Use a class when:

  • You want to reuse the same style across multiple elements.
  • You're building modular components that might appear more than once.
  • You want cleaner, more maintainable CSS without high specificity conflicts.

One thing to note: some developers avoid using IDs altogether in CSS because of their high specificity, which can make overriding styles tricky later on. But they still have valid uses, especially outside of styling — like in JavaScript or URL fragments.

So yeah, basically it comes down to uniqueness and reusability. ID for one, class for many. Not too complicated, but definitely important to get right.

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