rem和em的核心區(qū)別在於計(jì)算基準(zhǔn)不同。 rem始終基於根元素（通常是）的字體大小，適用於全局一致性場(chǎng)景如基礎(chǔ)字號(hào)、佈局間距；而em基於最近父元素的字體大小，適合需要局部比例縮放的組件內(nèi)部使用如按鈕圖標(biāo)、表單標(biāo)籤；使用rem可避免嵌套時(shí)的尺寸倍增問(wèn)題，並支持通過(guò)調(diào)整根字號(hào)實(shí)現(xiàn)整體縮放，而使用em需注意層級(jí)疊加可能導(dǎo)致的意外效果。
When building responsive and accessible websites, choosing the right unit for sizing elements in CSS matters. Two units that often come up in discussions are em and rem . While they might seem interchangeable at first glance, they behave differently and serve different purposes depending on your layout needs.
What's the basic difference?
The main difference between em and rem lies in what they're based on.
-
emis relative to the font size of its direct or nearest parent element . -
remstands for "root em" and is always relative to the font size of the root element , which is usually theelement.
This means that with em , sizes can compound if you're not careful—especially in deeply nested elements. With rem , everything stays consistent because it's tied directly to the root font size.
For example:
html {
font-size: 16px;
}
div {
font-size: 1.5em; /* 24px */
}
span {
font-size: 1.5em; /* 36px (based on parent div's 24px) */
} In this case, the span ends up much bigger than expected because each level inherits and scales the size.
When to use em
Use em when you want an element's size to scale relative to its parent —this is especially useful for UI components like buttons or cards where internal spacing should stay proportional even if the component's overall size changes.
Some practical uses:
- Icons inside buttons
- Padding/margin within a module or component
- Font sizes for labels inside form elements
Just keep in mind that nesting multiple em values can lead to unexpected results unless you carefully track inherited sizes.
When to use rem
Use rem when you want more predictable and consistent sizing across your site. It's ideal for things like:
- Base font sizes for body text
- Spacing (margins, padding) between major layout elements
- Widths and heights of larger containers
Because rem is always based on the root font size, it avoids compounding issues and makes global design changes easier. For instance, if you change the root font size, all rem -based measurements scale accordingly—great for accessibility features like allowing users to adjust default font sizes.
A common practice is setting a base font size like this:
html {
font-size: 16px;
} Then using rem for nearly everything else.
A few small but important details
One thing many developers miss early on is how browser defaults affect rem . Most browsers set the default <html> font size to 16px, so 1rem equals 16px by default—but this can vary if users have changed their settings.
Also, using media queries with rem can help maintain visual consistency. For example:
@media (min-width: 40rem) {
/* Adjust styles for larger screens */
}This way, breakpoints scale along with the root font size, keeping proportions intact.
Another tip: If you're working on a large project, consider using a CSS preprocessor or tool that helps convert pixel values into rem automatically—it reduces manual calculation errors.
基本上就這些。 Choosing between em and rem comes down to whether you need local scaling ( em ) or global consistency ( rem ). Both are powerful, just suited for different situations.
以上是比較CSS中的`em`和'rem'單位的詳細(xì)內(nèi)容。更多資訊請(qǐng)關(guān)注PHP中文網(wǎng)其他相關(guān)文章！
熱AI工具
Undress AI Tool
免費(fèi)脫衣圖片
Undresser.AI Undress
人工智慧驅(qū)動(dòng)的應(yīng)用程序，用於創(chuàng)建逼真的裸體照片
AI Clothes Remover
用於從照片中去除衣服的線上人工智慧工具。
Clothoff.io
AI脫衣器
Video Face Swap
使用我們完全免費(fèi)的人工智慧換臉工具，輕鬆在任何影片中換臉！
熱門文章
熱工具
記事本++7.3.1
好用且免費(fèi)的程式碼編輯器
SublimeText3漢化版
中文版，非常好用
禪工作室 13.0.1
強(qiáng)大的PHP整合開(kāi)發(fā)環(huán)境
Dreamweaver CS6
視覺(jué)化網(wǎng)頁(yè)開(kāi)發(fā)工具
SublimeText3 Mac版
神級(jí)程式碼編輯軟體(SublimeText3)
如何用PHP搭建社交分享功能 PHP分享接口集成實(shí)戰(zhàn)
Jul 25, 2025 pm 08:51 PM
在PHP中搭建社交分享功能的核心方法是通過(guò)動(dòng)態(tài)生成符合各平臺(tái)要求的分享鏈接。 1.首先獲取當(dāng)前頁(yè)面或指定的URL及文章信息；2.使用urlencode對(duì)參數(shù)進(jìn)行編碼；3.根據(jù)各平臺(tái)協(xié)議拼接生成分享鏈接；4.在前端展示鏈接供用戶點(diǎn)擊分享；5.動(dòng)態(tài)生成頁(yè)面OG標(biāo)籤優(yōu)化分享內(nèi)容展示；6.務(wù)必對(duì)用戶輸入進(jìn)行轉(zhuǎn)義以防止XSS攻擊。該方法無(wú)需複雜認(rèn)證，維護(hù)成本低，適用於大多數(shù)內(nèi)容分享需求。
PHP打造博客評(píng)論系統(tǒng)變現(xiàn) PHP評(píng)論審核與防刷策略
Jul 25, 2025 pm 08:27 PM
1.評(píng)論系統(tǒng)商業(yè)價(jià)值最大化需結(jié)合原生廣告精準(zhǔn)投放、用戶付費(fèi)增值服務(wù)（如上傳圖片、評(píng)論置頂）、基於評(píng)論質(zhì)量的影響力激勵(lì)機(jī)制及合規(guī)匿名數(shù)據(jù)洞察變現(xiàn)；2.審核策略應(yīng)採(cǎi)用前置審核 動(dòng)態(tài)關(guān)鍵詞過(guò)濾 用戶舉報(bào)機(jī)制組合，輔以評(píng)論質(zhì)量評(píng)分實(shí)現(xiàn)內(nèi)容分級(jí)曝光；3.防刷需構(gòu)建多層防禦：reCAPTCHAv3無(wú)感驗(yàn)證、Honeypot蜜罐字段識(shí)別機(jī)器人、IP與時(shí)間戳頻率限制阻止灌水、內(nèi)容模式識(shí)別標(biāo)記可疑評(píng)論，持續(xù)迭代應(yīng)對(duì)攻擊。
什麼是常見(jiàn)的CSS瀏覽器不一致？
Jul 26, 2025 am 07:04 AM
不同瀏覽器對(duì)CSS解析存在差異，導(dǎo)致顯示效果不一致，主要包括默認(rèn)樣式差異、盒模型計(jì)算方式、Flexbox和Grid佈局支持程度及某些CSS屬性行為不一致。 1.默認(rèn)樣式處理不一致，解決方法是使用CSSReset或Normalize.css統(tǒng)一初始樣式；2.舊版IE的盒模型計(jì)算方式不同，建議統(tǒng)一使用box-sizing:border-box；3.Flexbox和Grid在邊緣情況或舊版本中表現(xiàn)有差異，應(yīng)多測(cè)試並使用Autoprefixer；4.某些CSS屬性行為不一致，需查閱CanIuse並提供降級(jí)
如何用Mac搭建PHP Nginx環(huán)境 MacOS配置Nginx與PHP服務(wù)組合
Jul 25, 2025 pm 08:24 PM
Homebrew在Mac環(huán)境搭建中的核心作用是簡(jiǎn)化軟件安裝與管理。 1.Homebrew自動(dòng)處理依賴關(guān)係，將復(fù)雜的編譯安裝流程封裝為簡(jiǎn)單命令；2.提供統(tǒng)一的軟件包生態(tài)，確保軟件安裝位置與配置標(biāo)準(zhǔn)化；3.集成服務(wù)管理功能，通過(guò)brewservices可便捷啟動(dòng)、停止服務(wù)；4.便於軟件升級(jí)與維護(hù)，提升系統(tǒng)安全性與功能性。
描述'垂直align”屬性及其典型用例
Jul 26, 2025 am 07:35 AM
1.ItAdjustSelementsLikeImagesRikeImagesOrformInputswithIntExtLineSustLineSlineSlineSlineSlikeLikeLikeBaseline，中間，Super，Super，Super和Sub.2.intablebecells，ItControlScontentalStalteNtalmscontentalMedwithThtop，Middle，Middle，Midder，Midder，經(jīng)常
什麼是口音色的物業(yè)？
Jul 26, 2025 am 09:25 AM
accent-color是CSS中用於自定義復(fù)選框、單選按鈕和滑塊等表單元素高亮顏色的屬性；1.它直接改變表單控件選中狀態(tài)的默認(rèn)顏色，如將復(fù)選框的藍(lán)色勾選標(biāo)記改為紅色；2.支持的元素包括type="checkbox"、type="radio"和type="range"的輸入框；3.使用accent-color可避免複雜的自定義樣式和額外DOM結(jié)構(gòu)，保持原生可訪問(wèn)性；4.現(xiàn)代瀏覽器普遍支持，舊瀏覽器需降級(jí)處理；5.設(shè)置accent-col
如何將SCSS編譯到CSS？
Jul 27, 2025 am 01:58 AM
installdartsassvianpmafterinstallingnode.jsusingnpminstall-gsass.2.compilescsstocssssusingthecommandSassInput.scsssoutput.css.3。 useass - watchinput.scssoutput.csstoauto-compileonsave.4.watchentirefolderswithsass-watchscss：css.5.usepartialswith_prefixfo
如何更改CSS中的文本顏色？
Jul 27, 2025 am 04:25 AM
要改變CSS中文本顏色，需使用color屬性；1.使用color屬性可設(shè)置文本前景色，支持顏色名稱（如red）、十六進(jìn)制碼（如#ff0000）、RGB值（如rgb(255,0,0)）、HSL值（如hsl(0,100%,50%)）以及帶透明度的RGBA或HSLA（如rgba(255,0,0,0.5)）；2.可將顏色應(yīng)用於包含文本的任何元素，如h1至h6標(biāo)題、段落p、鏈接a（需注意a:link、a:visited、a:hover、a:active不同狀態(tài)的顏色設(shè)置）、按鈕、div、span等；3.最
