媒體查詢是一種CSS功能，允許根據(jù)設(shè)備的屏幕尺寸、分辨率或方向應(yīng)用不同的樣式，從而實現(xiàn)響應(yīng)式網(wǎng)頁設(shè)計。其核心作用是通過條件判斷優(yōu)化不同設(shè)備上的佈局顯示效果。例如，當(dāng)屏幕寬度小於768px時隱藏菜單以適配移動設(shè)備。它幫助開發(fā)者在不修改HTML的前提下調(diào)整佈局結(jié)構(gòu)、字體大小、元素可見性及圖片切換。典型應(yīng)用場景包括手機（480px）、平板（768px）和桌面設(shè)備（1024px或1200px）的適配。建議採用移動優(yōu)先策略，並結(jié)合內(nèi)容需求靈活設(shè)置斷點。使用時需注意測試實際屏幕寬度、合理搭配min-width與max-width、避免設(shè)備特定化、配合流體網(wǎng)格與彈性圖片，並務(wù)必設(shè)置viewport元標(biāo)籤以確保正確縮放。

Media queries let you apply different styles based on a device's screen size, resolution, or orientation. That's the core idea behind responsive web design — showing the best possible layout for whatever screen someone is using.

What Exactly Are Media Queries?

They're part of CSS and work like conditions: if the screen meets certain criteria (like width or height), then specific styles get applied. Think of them as a way to ask the browser questions — like “Is this screen narrower than 768px?” — and change the layout accordingly.

For example:

 @media only screen and (max-width: 768px) {
  .menu {
    display: none;
  }
}

This bit of code hides the menu on smaller screens — maybe to make room for a mobile-friendly hamburger menu instead.

How Do They Help With Responsive Design?

The main benefit is that you can tailor layouts without changing HTML. Here are a few ways media queries do that:

• Adjust layout structure : Stack columns vertically on small screens.
• Change font sizes : Make text more readable on phones by bumping up the size.
• Hide or show elements : Like sidebars or navigation menus.
• Switch images : Use smaller images or different ones depending on screen size.

You don't need separate pages for desktop and mobile — just one HTML file with flexible styling.

When Should You Use Them?

Mostly when building sites that should look good across devices. A typical approach is to start with a mobile-first strategy, meaning your base styles target smaller screens, then use media queries to enhance the layout for larger ones.

Common breakpoints (widths where styles change) include:

• 480px (phones)
• 768px (tablets)
• 1024px (small desktop/laptop)
• 1200px (larger screens)

But you shouldn't just follow fixed numbers blindly — adjust based on content. If your layout starts looking off at a certain width, that's your breakpoint.

A Few Tips to Keep in Mind

• Always test designs at actual screen widths, not just predefined sizes.
• Use min-width and max-width together for more control.
• Avoid device-specific targeting unless absolutely necessary.
• Combine media queries with fluid grids and flexible images for full responsiveness.

One thing that's easy to miss: forgetting to set the viewport meta tag in HTML. Without it, mobile browsers won't scale properly:

 <meta name="viewport" content="width=device-width, initial-scale=1">

That's basically how media queries help make websites respond well to different screens. It's not magic — just smart conditional styling.

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