Have you ever thought about differences between CSS units PX, EM, REM, %, VW, and VH. Don't worry, our simple guide. Perfect for making your website look great on any device!
When it comes to web design, understanding different units of measurement is crucial. In this article, we will explore the differences between the most commonly used units: PX, EM, REM, %, VW, and VH. By the end, you'll have a clear understanding of when and how to use each unit in your web designs.
What is a Pixel?
In CSS, a pixel (px) is a unit of measurement for size. It's often considered the building block of digital imagery. A pixel is effectively a single point in a raster image and is used in web design to represent a fixed unit of measurement.
Using Pixels in Layout, Font, and Positioning
1. Layout: Pixels are commonly used to specify fixed dimensions for elements like divs, headers, or footers.
Example Code:
css
.container {
width: 300px;
height: 200px;
}2. Font: Pixels provide a way to set exact font sizes.
Example Code:
css
p {
font-size: 16px;
}
3. Positioning: Pixels can be used to precisely position elements.
Example Code:
css
.box {
position: absolute;
left: 50px;
top: 100px;
}
Pros and Cons of Using Pixels
While pixels offer precision and consistency, they fall short in responsiveness and accessibility. It's important to balance their use with relative units like EM or REM for a more flexible and accessible web design.
Pros:
- Precision: Pixels allow for precise control over the sizing and positioning of elements.
- Consistency: They offer a consistent size across different browsers and devices.
Cons:
- Lack of Responsiveness: Pixel-based layouts don't adapt well to different screen sizes, potentially leading to issues on mobile devices.
- Accessibility Concerns: Using pixels for font sizes can limit the ability of users to adjust text size for readability.
What is EM?
In CSS, an `em` is a relative unit of measurement used for font sizes, spacing, and layout design. It is based on the font size of the element it is applied to, or the parent element's font size if not specified. This makes `em` adaptable to changes in design and user settings, providing a more fluid and responsive approach.
Using EMs in Font Sizing and Spacing
1. Font Sizing: EMs are particularly effective for typography, allowing text size to scale relative to the parent element's font size.
Example Code:
css
p {
font-size: 1.5em; /* 150% of the parent element's font size */
}
2. Spacing: EMs are also used for setting margins and padding, which scale with the element's font size.
Example Code:
css
.container {
padding: 2em; /* Padding relative to the container's font size */
}
Pros and Cons of Using EMs
While EMs offer scalability and flexibility, particularly for typography, their relative nature demands careful management in complex layouts to ensure consistent sizing.
Pros:
- Scalability: Scales with the font size, making it suitable for responsive typography and spacing.
- Flexibility: Adapts to changes in parent element's font size, offering a more dynamic layout.
Cons:
- Complexity in Nested Structures: Can lead to unexpected sizes due to compounding effect in nested elements.
- Inconsistency: The size of elements can vary depending on their position in the DOM, which may cause inconsistent sizing.
What is REM?
In CSS, `rem` stands for "Root EM." It is a relative measurement unit that refers to the font size of the root element of the document, which is usually the `<html>` element. Unlike `em`, which is based on the font size of the parent element, `rem` provides a way to size things consistently across your entire document based on a single reference point.
Using REMs in Web Design
1. Font Sizing: REM is particularly useful for setting consistent font sizes across your website, as it allows for uniform scaling based on the root element's size.
Example Code:
css
html {
font-size: 16px; /* Setting the root font-size */
}
body {
font-size: 1.6rem; /* 16px if the root font-size is 10px */
}
2. Spacing: REM units are also great for defining consistent margins, paddings, and other spacing elements, ensuring uniformity regardless of where they are used in the document.
Example Code:
css
.container {
padding: 2rem; /* This will always be relative to the root font size */
}
Pros and Cons of Using REMs
When it comes to sizing with REM units in CSS, there are clear benefits and some limitations to keep in mind. REMs offer a streamlined way to size elements, but this simplicity also comes with its own set of challenges.
Pros:
- Consistency: Ensures uniformity in sizing throughout the website, as everything is based on the root element's font size.
- Accessibility: Better for accessibility, as REMs scale appropriately when users change their browser’s default font size settings.
Cons:
- Less Control in Nested Elements: Unlike `em`, `rem` does not allow for scaling relative to parent elements, which can be limiting in certain design scenarios.
What is % (Percentage)?
In CSS, the `%` unit is a relative measurement that refers to a portion of a parent element's size. It's commonly used in defining layout properties such as width, height, padding, and margin, making it ideal for creating flexible and responsive web designs.
Using % in Web Design
1. Layout: Percentages are perfect for fluid layouts, allowing elements to adjust their size relative to their parent container.
Example Code:
css
.container {
width: 80%; /* Takes up 80% of the parent element's width */
}
2. Spacing: `%` can also be used for margins and padding to create spacing that adapts to the size of the parent element.
Example Code:
css
.content {
margin-left: 5%; /* Margin is 5% of the parent element's width */
}
Pros and Cons of Using %
Percentage units offer considerable advantages in terms of responsiveness and fluidity, their relative nature requires careful consideration in complex layouts to avoid unexpected results.
Pros:
- Responsiveness: Adapts to the changing size of parent elements, perfect for responsive designs.
- Flexibility: Useful in layouts where relative sizing is more practical than fixed sizing.
Cons:
- Dependency on Parent: The effectiveness of `%` depends on the size of the parent element, which can sometimes lead to unpredictability.
- Complexity in Nested Layouts: In deeply nested structures, calculating the size can become complex due to the compounding effect.
What are VW and VH?
`VW` (Viewport Width) and `VH` (Viewport Height) are CSS units that are relative to the size of the viewport. `1vw` is equal to 1% of the viewport's width, while `1vh` is 1% of the viewport's height. These units are especially useful in creating responsive designs that adapt to different screen sizes.
Using VW and VH in Web Design
1. Full-Screen Sections: VW and VH are excellent for creating elements that cover the full viewport, such as hero images or full-page sections.
Example Code:
css
.hero-section {
width: 100vw;
height: 100vh; /* Covers the entire viewport */
}
2. Responsive Sizing: They can be used to size elements relative to the viewport, which is particularly useful for responsive typography and layout design.
Example Code:
css
.responsive-text {
font-size: 5vw; /* Adjusts size based on viewport width */
}
Pros and Cons of Using VW and VH
Each of these units, `VW`, and `VH`, play a vital role in modern web design, offering different ways to create responsive and flexible layouts. Understanding when and how to use each can significantly enhance the usability and aesthetic of a website.
Pros:
- Viewport Relative: Offers a direct way to size elements based on the viewport, aiding in creating responsive designs.
- Versatile: Useful for both typography and layout, particularly in full-screen elements.
Cons:
- Viewport Dependency: Sizes can vary dramatically on different devices due to varying viewport sizes.
- Overlapping and Clipping Issues: Especially with VH, elements might overlap or get clipped on smaller screens.
Ideal use cases of Px, Em, Rem, %, Vw and Vh
Here are examples and explanations for each CSS unit type, showing their ideal use cases and potential consequences of using different units.
PX (Pixels)
Pixels provide precise control for fixed-size elements, making them perfect for elements where exact dimensions are crucial.
HTML:
html
<div class='fixed-size-box'></div>CSS:
css
.fixed-size-box {
width: 200px;
height: 100px;
background-color: lightblue;
}
Consequence: Using 'em' or '%' would cause the box size to change relative to parent font size or screen width, leading to inconsistencies.
Full-Code Try it Yourself for PX (Pixels)
<!DOCTYPE html>
<html>
<head>
<style>
.fixed-size-box {
background-color: lightblue;
width: 200px;
height: 100px;
}
</style>
</head>
<body>
<div class='fixed-size-box'></div>
</body>
</html>
EM
EM units, relative to the font size of their parent element, are ideal for typography and scaling elements in relation to text.
HTML:
html
<div class='em-padding-box'><p>Content here</p></div>
CSS:
css
.em-padding-box {
padding: 2em;
border: 1px solid black;
}
.em-padding-box p {
font-size: 1em;
}
Consequence: Using 'px' disconnects padding size from text size, potentially harming layout harmony as text size changes.
Full-Code Try it Yourself for EM
<!DOCTYPE html>
<html>
<head>
<style>
.em-padding-box {
padding: 2em;
border: 1px solid black;
}
.em-padding-box p {
font-size: 1em;
}
</style>
</head>
<body>
<div class='em-padding-box'>
<p>Content here</p>
</div>
</body>
</html>
REM
REM units provide consistent typography across the website, scaling based on the root element's font size.
HTML:
html
<p class='uniform-text'>Uniform Text</p>
CSS:
css
html {
font-size: 16px;
}
.uniform-text {
font-size: 2rem;
}
Consequence: Using 'em' would result in varying text sizes, dependent on the parent element's font size.
Full-Code Try it Yourself for REM
<!DOCTYPE html>
<html>
<head>
<style>
html {
font-size: 16px;
}
.uniform-text {
font-size: 2rem;
}
</style>
</head>
<body>
<p class='uniform-text'>Uniform Text</p>
</body>
</html>
%
Percentage units adapt to their parent element's size, making them perfect for responsive layouts.
HTML:
html
<div class='responsive-box'></div>
CSS:
css
.responsive-box {
width: 50%;
height: 100px;
background-color: lightcoral;
}
Consequence: A fixed unit like 'px' would render the box non-responsive, potentially disrupting the layout on different screens.
Full-Code Try it Yourself for %
<!DOCTYPE html>
<html>
<head>
<style>
.responsive-box {
background-color: lightcoral;
width: 50%;
height: 100px;
}
</style>
</head>
<body>
<div class='responsive-box'></div>
</body>
</html>
VW and VH
Viewport width (VW) and height (VH) units are based on the browser window size, ideal for full-screen sections or responsive elements.
HTML:
html
<div class='full-screen-section'></div>
CSS:
css
.full-screen-section {
width: 100vw;
height: 100vh;
background-color: lightgreen;
}
Consequence: Fixed units like 'px' prevent adaptation to different viewport sizes, possibly causing overflow or unused space.
Full-Code Try it Yourself for VW and VH
<!DOCTYPE html>
<html>
<head>
<style>
.full-screen-section {
background-color: lightgreen;
width: 100vw;
height: 100vh;
}
</style>
</head>
<body>
<div class='full-screen-section'></div>
</body>
</html>
These examples demonstrate how choosing the right CSS unit for the specific context of your web design can significantly impact the effectiveness and responsiveness of the layout.
Complex usage of Px, Em, Rem, %, Vw and Vh
We created a complex webpage for beginners to understand all unit types and their usage as a whole you can find all unit types at the code. Start debug on your ide and tweak some codes to udnerstand how units effect the overall page.
<!DOCTYPE html>
<html>
<head>
<style>
:root {
font-size: 16px;
}
body {
font-family: Arial, sans-serif;
font-size: 1rem; /* Using REM */
margin: 0;
padding: 0;
background-color: #f2f2f2;
}
/* Header */
.header {
background-color: #333;
color: #fff;
padding: 2rem 0; /* Using REM */
text-align: center;
}
/* Navigation */
.navbar {
background-color: #444;
overflow: hidden;
}
.navbar a {
float: left;
display: block;
color: #fff;
text-align: center;
padding: 1rem 1em; /* Using EM */
text-decoration: none;
}
/* Container */
.container {
width: 80vw; /* Using VW */
margin: 1rem auto; /* Using REM */
background-color: #fff;
box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
}
/* Main Content */
.content {
padding: 2rem; /* Using REM */
float: left;
width: 70%; /* Using % */
}
/* Sidebar */
.sidebar {
width: 30%; /* Using % */
float: left;
background-color: #f2f2f2;
padding: 2rem; /* Using REM */
}
/* Footer */
.footer {
background-color: #333;
color: #fff;
text-align: center;
padding: 1rem 0; /* Using REM */
clear: both;
}
</style>
</head>
<body>
<div class="header">
<h1>Professional Responsive Page</h1>
</div>
<div class="navbar">
<a href="#">Home</a>
<a href="#">About</a>
<a href="#">Services</a>
<a href="#">Contact</a>
</div>
<div class="container">
<div class="content">
<h2>Main Content</h2>
<p>This is the main content of the webpage. It adapts to different screen sizes using various CSS units.</p>
</div>
<div class="sidebar">
<h2>Sidebar</h2>
<p>This is the sidebar content. It uses percentage (%) for its width.</p>
</div>
</div>
<div class="footer">
<p>© 2023 Professional Responsive Page</p>
</div>
</body>
</html>
Quiz - CSS Units PX, EM, REM, %, VW, and VH
1- What is the abbreviation "PX" in CSS units, and how is it commonly used?
Answer: PX stands for "Pixels" in CSS units. It is commonly used to specify fixed dimensions for elements like divs, headers, or footers.
2- In CSS, what does "EM" represent as a unit of measurement, and where is it often used?
Answer: EM is a relative unit of measurement in CSS. It is often used for font sizes, spacing, and layout design, scaling relative to the parent element's font size.
3- What does "REM" stand for in CSS units, and how does it differ from "EM"?
Answer: REM stands for "Root EM." It is a relative unit based on the root element's font size, typically the <html> element. Unlike EM, which is based on the parent element's font size, REM provides consistency across the entire document.
4- What does the "%" unit represent in CSS, and why is it useful in web design?
Answer: "%" represents a percentage unit in CSS, referring to a portion of a parent element's size. It is useful for defining responsive layouts and adapting elements to their parent container's size.
5- What are "VW" and "VH" in CSS units, and when are they commonly used?
Answer: VW (Viewport Width) and VH (Viewport Height) are CSS units relative to the size of the viewport. They are commonly used for creating full-screen sections and responsive designs.
6- What are some pros of using "PX" (Pixels) as a CSS unit in web design?
Answer: Pros of using PX include precision and consistency in sizing and positioning elements.
7- What are the advantages of using "EM" units for font sizing and spacing in CSS?
Answer: EM units offer scalability and flexibility, particularly for typography, as they scale with the parent element's font size.
8- What is the primary benefit of using "REM" units in CSS for font sizing and spacing?
Answer: REM units provide consistency in typography across a website, scaling based on the root element's font size.
9- What is the main advantage of using "%" units in CSS layouts, and when should you be cautious about their use?
Answer: "%" units are advantageous for responsiveness and fluidity. However, they depend on the size of the parent element, which can lead to unpredictability in complex layouts.
10- How do "VW" and "VH" units contribute to responsive web design, and what are potential challenges when using them?
Answer: VW and VH units are essential for responsive designs, as they size elements relative to the viewport. However, they may lead to varying sizes on different devices, and there can be overlapping or clipping issues with VH.
Homework - CSS Units PX, EM, REM, %, VW, and VH
In a web development project, you are tasked with creating a responsive webpage that demonstrates the use of various CSS units such as pixels (PX), em, rem, percentages (%), viewport width (VW), and viewport height (VH) in different contexts. You want to ensure that the main content and the sidebar appear side by side horizontally.
Based on the explanation, how can you achieve the desired horizontal layout for the main and sidebar elements using CSS, particularly utilizing flexbox, while maintaining responsiveness?
Answer
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>CSS Units Example</title>
<style>
/* Root-level CSS variables */
:root {
--header-bg-color: #4CAF50;
--font-size-em: 2em;
--font-size-rem: 1.5rem;
--font-size-vw: 4vw;
--sidebar-width: 30vw;
}
/* Reset some default styles for better layout */
body, h1, h2, h3, p, ul, li {
margin: 0;
padding: 0;
}
/* Improved Header styles with added height and centered text */
header {
background-color: var(--header-bg-color);
color: white;
padding: 20px 0;
text-align: center;
font-size: var(--font-size-em);
}
/* Navigation styles using EM for font size and centered links */
nav {
background-color: #333;
color: white;
font-size: var(--font-size-em);
text-align: center;
}
ul {
list-style-type: none;
padding: 0;
}
ul li {
display: inline;
margin-right: 20px;
}
ul li a {
color: white;
text-decoration: none;
}
/* Improved Main content styles with centered text */
main {
text-align: center;
padding: 20px;
}
article {
margin: 20px auto;
max-width: 800px;
}
/* Sidebar styles using VW for font size and VH for padding */
.sidebar {
font-size: var(--font-size-vw);
width: var(--sidebar-width);
background-color: #f2f2f2;
padding: 5vh 20px;
}
/* Responsive styles using media queries */
@media (max-width: 768px) {
main {
font-size: 1.2rem;
}
.sidebar {
font-size: 3vw;
width: 80%;
margin: 0 auto;
}
}
/* Footer styles */
footer {
background-color: #333;
color: white;
text-align: center;
padding: 20px;
clear: both;
}
/* Flexbox for horizontal layout */
.flex-container {
display: flex;
}
.main-content {
flex: 70%;
}
.sidebar {
flex: 30%;
}
</style>
</head>
<body>
<header>Header (Background color)</header>
<nav>
<ul>
<li><a href="#">Link 1</a></li>
<li><a href="#">Link 2</a></li>
<li><a href="#">Link 3</a></li>
</ul>
</nav>
<div class="flex-container">
<main class="main-content">
<article>
<h2>Main Content Title</h2>
<p>This is a paragraph of text.</p>
<img src="https://via.placeholder.com/300" alt="Placeholder Image">
</article>
</main>
<div class="sidebar">
<h3>Sidebar Title</h3>
<p>This is additional information.</p>
</div>
</div>
<footer>Footer (Copyright information)</footer>
</body>
</html>
FAQ
1- What is the distinction between PX, EM, REM, %, VW, and VH units in CSS?
PX (Pixels): These are like the precise architects of CSS, defining element size meticulously.
EM: These units are CSS's relatives, adjusting according to their parent's font size, often used for font and spacing.
REM (Root EM): Relatives too, but anchored to the root element's font size, ensuring uniformity.
% (Percentage): CSS's adaptable performers, scaling based on their parent's size, ideal for responsive designs.
VW (Viewport Width): These units dance to the viewport's width, adapting gracefully to varying screens.
VH (Viewport Height): Similar to VW, but they follow the viewport's height, crucial for responsive designs.
2- When is it best to employ PX units in CSS, and what benefits do they bring?
PX units shine when precision matters, such as crafting pixel-perfect headers, footers, or fixed-size elements.
3- How do EM units function in CSS for font sizing, and why are they referred to as relatives?
EM units are like family members; they inherit their size from the parent element's font, adapting to changes in typography and layout. They're "relatives" because they depend on their parent's font size.
4- What's the significance of REM units in CSS, and how do they differ from EM units?
REM units play a vital role, based on the root element's font size, ensuring consistent sizing across the entire document. This sets them apart from EM units, which rely on parent font sizes.
5- When is the perfect time to employ percentage (%) units in CSS layouts, and what advantages do they offer for responsiveness?
Percentage units are stars in responsive design, adjusting gracefully to their parent's size, making layouts flexible and adaptable.
6- Can you explain VW and VH units in CSS, and where are they typically used in web design?
7- What are the pros and cons of using PX units for defining fixed dimensions in CSS layouts?
PX units offer meticulous control over sizing, ensuring precision.
However, they lack the adaptability and responsiveness needed for different screen sizes.
8- What are the benefits of using EM units for typography and spacing in CSS?
EM units are versatile performers, scaling beautifully with their parent's font size, making them perfect for typography and spacing.
9- How can I maintain consistency in font sizing across my website using REM units?
By setting the root element's font size with REM units, you can ensure harmony in text sizes, aiding in responsive design.
10- What challenges or limitations might I encounter when using percentage (%) units for layout design in CSS?
Percentage units, though flexible, can be unpredictable in complex layouts as they depend on their parent's sizes.
11- How do VW and VH units contribute to crafting responsive web designs, and what precautions should I take when using them?
VW and VH units are essential for responsive designs, but they can lead to varying sizes on different devices. Beware of potential overlap or clipping with VH.
12- What's the purpose of using CSS variables (custom properties) in the provided code examples?
CSS variables act as the conductors of harmony, allowing for consistent definition and reuse of values, simplifying style maintenance.
13- How can I make the sidebar element responsive in the code example?
To make the sidebar responsive, use media queries to adjust its size and font size based on the viewport's width.
14- What are media queries, and how do they enable responsive design in the provided code?
Media queries act as the responsive designers, applying specific styles based on the device's characteristics, ensuring adaptability.
15- Could you elucidate the role of flexbox in achieving the horizontal layout of the main content and sidebar in the code example?
Flexbox serves as the choreographer of the horizontal dance between the main content and sidebar, adapting gracefully to different screen sizes by defining their flex properties within a flex container.
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