What are the relative length units in css? Introduction to commonly used relative units em and rem-CSS Tutorial-php.cn

Home

Web Front-end

CSS Tutorial

What are the relative length units in css? Introduction to commonly used relative units em and rem

青灯夜游

Oct 16, 2018 pm 04:05 PM

emrem

There are many length units in css, which can be described as diverse, but they can basically be divided into three categories: relative length units, absolute length units and visual area percentage length units. This article will tell you what units are included in the relative length unit category and introduce how to use commonly used relative units. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

The relative length units in css include: em, rem, points, pica, ex, ch, etc. Let’s introduce the two commonly used units in relative length: how to use the em and rem units. .

css length unit em unit

em is a relative font length unit, and its unit length is based on the vertical length of the text of the element. decided. For example: 1em is equivalent to the current font size (font-size attribute), then 2em is equivalent to twice the current font size. If used for other attributes (width, height), it is relative to the font-size of the element itself. It can be used to set width, height, line-height, margin, padding, border and other styles.

Let’s look at a simple example in detail to understand em.

<!DOCTYPE html>
<html>

	<head>
		<meta charset="UTF-8">
		<style>
			div {
				font-size: 40px;
				width: 10em;
				/* 400px */
				height: 10em;
				border: solid 1px black;
			}
			
			p {
				font-size: 0.5em;
				/* 20px */
				width: 10em;
				/* 200px */
				height: 10em;
				border: solid 1px red;
			}
			
			span {
				font-size: 0.5em;
				width: 10em;
				height: 10em;
				border: solid 1px blue;
				display: block;
			}
		</style>

	</head>

	<body>
		<div>
			我是父元素div
			<p>
				我是子元素p
				<span>我是孙元素span</span>
			</p>
		</div>
	</body>
	</body>

</html>

Rendering:

What are the relative length units in css? Introduction to commonly used relative units em and rem

Characteristics of em:

The value of the em unit is not Fixed, the em of the font size of the child element is relative to the font size of the parent element; the width/height/padding/margin of the
element using em is relative to the font-size of the element.

css length unit rem unit

rem is a new relative font length unit in CSS3, which is only relative The root element, that is, the font size of the html element is used to determine its length, which is an essential length unit for mobile pages.

<!DOCTYPE html>
<html>

	<head>
		<meta charset="UTF-8">
		<style>
			html {
				font-size: 16px;
			}
			
			.div1 {
				font-size: 3rem;
			}
			
			.div2 {
				font-size: 0.5rem;
			}
		</style>

	</head>

	<body>

		<div class="div1">
			div1---48px
			<div class="div2">
			    div2---8px
			</div>
		</div>
	</body>
	</body>

</html>

Rendering:

What are the relative length units in css? Introduction to commonly used relative units em and rem

#In the example, the font size of html is a fixed size of 16px, and the font size of div1 is set to 3rem, and: 3rem = 16px * 3 = 48px, so the font size of div1 is 48;

sets the font size of div2 to 0.5rem, and: 0.5rem = 16px * 0.5 = 8px, so the font size of div2 is 8px.

Comparison between em and rem

Let’s take a look at the difference between em and rem through a simple example

<!DOCTYPE html>
<html>

	<head>
		<meta charset="UTF-8">
		<style>
			html {
				font-size: 16px;
			}
			
			body {
				font-size: 8px;
			}

			.div1 {
				font-size: 3rem;
				/* 3rem = 16px * 3 = 48px */
				width: 20em;
				/* 20em = 48px * 20 = 960px */
				height: 20rem;
				/* 10rem = 16px * 20 = 320px */
				border: 1px solid red;
			}
			
			.div2 {
				font-size: 0.5em;
				/* 0.5rem = 48px * 0.5 = 24px */
				width: 10em;
				/* 10em = 48px * 10 = 480px */
				height: 10rem;
				/* 10rem = 16px * 10 = 160px */
				border: 1px solid black;
			}
		</style>

	</head>

	<body>
		<div>
			html设置字体大小为16px,body设置为8px。<br />
			div1的字体大小为3rem(3rem = 16px * 3 = 48px)
		</div>
		<div class="div1">
			
			div1--宽20em(960px),高20rem(320px)
			<div class="div2">
				div2<br />
				宽10em(480px)<br />
				高10rem(160px)
			</div>
		</div>
	</body>
	</body>

</html>

Rendering:

What are the relative length units in css? Introduction to commonly used relative units em and rem

Note: The font-size of the

div1 box is 3rem, for reference It is the font-size of the root element html; the width of the

div1 box is 20em. Because it has the font-size attribute, the reference text is its own font-size;

height of the div1 box It is 3rem, and the reference is the font-size of the root element html; the font-size of the

div2 box is 0.5em, and the reference is the font-size of its parent element div1 box;

div2 The height of the box is 10rem, and the reference text is the font-size of the root element html;

The width of the div2 box is 10em, and the reference text is the font-size of the parent element div1 box.

Summary : The above is the entire content of this article, I hope it will be helpful to everyone's study. For more related tutorials, please visit CSS Basics Video Tutorial, CSS3 Video Tutorial, bootstrap Video Tutorial!

The above is the detailed content of What are the relative length units in css? Introduction to commonly used relative units em and rem. For more information, please follow other related articles on the PHP Chinese website!

Statement

The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

REM(全称REMME)是什么币？Feb 21, 2024 pm 05:00 PM

REMME是什么币？REMME是一个基于区块链技术的加密货币，致力于提供高度安全且去中心化的网络安全和身份验证解决方案。该项目旨在利用分布式加密技术来增强和简化用户身份验证流程，从而提升安全性和效率。REMME的创新之处在于其借助区块链的不可篡改性和透明性，为用户提供了更可靠的身份验证方式。通过将身份验证信息存储在区块链上，REMME消除了中心化身份验证系统的单点故障，并降低了数据被盗或篡改的风险。这种基于区块链的身份验证方法不仅更安全可靠，而且还能够为用户REMME的背景在当前数字化时代，网络

CSS布局单位的演变与应用：从像素到根据根元素字体大小的相对单位Jan 05, 2024 pm 05:41 PM

从px到rem：CSS布局单位的演变与应用引言：在前端开发中，我们经常需要用到CSS来实现页面布局。在过去的几年间，CSS布局单位也经历了演变和发展。最开始我们使用的是像素（px）作为单位来设置元素的大小和位置。然而，随着响应式设计的兴起和移动设备的普及，像素单位逐渐暴露出一些问题。为了解决这些问题，新的单位rem应运而生，并逐渐被广泛应用于CSS布局中。一

CSS 单位属性优化技巧：em，rem，px 和 vw/vhOct 20, 2023 pm 12:54 PM

CSS单位属性优化技巧：em，rem，px和vw/vh引言：在网页设计和开发中，CSS单位属性起着非常重要的作用。正确选择和使用合适的单位属性可以使得页面在不同的设备和屏幕尺寸下展示得更加美观和一致。本文将介绍一些常用的CSS单位属性，并提供具体的代码示例来帮助读者更好地掌握这些优化技巧。em单位：em单位是相对于父元素的字体大小来计算的。例如

css中的em是什么单位Dec 07, 2023 pm 02:56 PM

CSS中的em是一个相对长度单位，它是相对于元素的字体大小来计算的，1em等于当前元素的字体大小，如果应用在字体大小上，1em将等于父元素的字体大小。

html5中px和em的区别是什么Aug 19, 2022 pm 05:36 PM

区别：1、单位长度不同，px是数字化图像长度单位，em是字符宽度的倍数；2、相对对象不同，px是相对于显示器屏幕分辨率而言的，em是相对于当前对象内文本的字体尺寸。3、px的值是固定的，指定是多少就是多少，计算比较容易；em的值不是固定的，并且em会继承父级元素的字体大小。

CSS 单位属性指南：em，rem，px 和 vw/vhOct 25, 2023 am 10:37 AM

CSS单位属性指南：em，rem，px和vw/vh在编写CSS样式时，选择合适的单位属性是非常重要的。本文将介绍几种常用的单位属性：em，rem，px和vw/vh，并提供具体的代码示例。emem（字体尺寸单位）是相对于父元素字体尺寸的单位。如果父元素的字体尺寸为16px，1em就等于16px。当em用于其他属性（如宽度、高度等）时，也是相对于父元素

Vue移动端解决1px像素问题的方法Jun 30, 2023 pm 06:21 PM

Vue开发中如何解决移动端1px像素问题随着移动互联网的快速发展，移动端应用的需求日益增加。然而，移动设备屏幕的尺寸和像素密度的多样性给开发者带来了一定的挑战。其中一个常见的问题是移动端1px像素问题。本文将介绍如何在Vue开发中解决移动端1px像素问题。问题的根源移动端1px像素问题的根源在于移动设备的物理像素和设备独立像素的不匹配。设备独立像素（CSS像

常用的CSS长度单位有哪些？Feb 19, 2024 pm 09:10 PM

CSS最常用的长度单位有像素(px)、百分比(%)、另外还有rem、em、vh、vw、pt、cm、mm、in等。这些单位可以用来设置元素的宽度、高度、边框尺寸、字体大小等。像素(px)单位是最常用的单位之一。它是固定的长度单位，相对于电子屏幕的物理像素来计算。以下是一个代码示例：div{width:200px;heigh

See all articles