Css Module 43

 

Css Module 43

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Css Module 43

  Module 43 : Using SCSS preprocessors 

 Module Objectives:

By the end of this module, learners will be able to:

Understand the role of preprocessors in modern CSS development.

Use variables to store reusable values.

Create and apply mixins for reusable chunks of CSS.

Write custom functions for dynamic CSS logic.

Apply SCSS in a project using experiments.

1. Introduction to CSS Preprocessors

        

CSS preprocessors like SASS (Syntactically Awesome Style Sheets) extend CSS with features like variables, nesting, mixins, and functions.

Why Use SASS?

Maintainability: Cleaner and modular code.

Reusability: Avoid repetition.

Logic in Stylesheets: Conditionals, loops, and functions.

2. Variables in SASS/SCSS

Explanation:

Variables store values (e.g., colors, spacing, fonts) that you can reuse throughout your stylesheets.

Syntax:

scss

code

$primary-color: #3498db; $padding-base: 1rem; body { background-color: $primary-color; padding: $padding-base; }

Example:

scss

 code

$font-stack: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif; $heading-color: #2c3e50; h1, h2, h3 { font-family: $font-stack; color: $heading-color; }

Exercise 1:

Task: Create a button using variables for background color, text color, and padding.

Expected Output:

scss

code

$btn-bg: #e74c3c; $btn-text: #fff; $btn-padding: 10px 20px; .button { background-color: $btn-bg; color: $btn-text; padding: $btn-padding; border: none; border-radius: 5px; }

3. Mixins in SASS/SCSS

        

Explanation:

Mixins let you define a group of CSS declarations that you can reuse throughout your stylesheet.

Syntax:

scss

 code

@mixin border-radius($radius) { border-radius: $radius; -webkit-border-radius: $radius; -moz-border-radius: $radius; } .box { @include border-radius(10px); }

Example:

scss

 code

@mixin flex-center { display: flex; justify-content: center; align-items: center; } .container { @include flex-center; height: 100vh; }

Exercise 2:

Task: Create a mixin for a box-shadow with default and custom parameters.

Expected Output:

scss

code

@mixin box-shadow($x: 0px, $y: 2px, $blur: 5px, $color: rgba(0, 0, 0, 0.1)) { box-shadow: $x $y $blur $color; } .card { @include box-shadow; } .alert { @include box-shadow(0px, 4px, 10px, rgba(255, 0, 0, 0.2)); }

4. Functions in SASS/SCSS

Explanation:

Functions perform calculations and return values. Great for dynamic values like spacing, font sizes, or color manipulation.

Syntax:

scss

code

@function em($px, $base: 16) { @return ($px / $base) * 1em; } .text { font-size: em(18); }

Example:

scss code

@function spacing($multiplier) { @return $multiplier * 8px; } .card { padding: spacing(2); // 16px margin: spacing(3); // 24px }

Exercise 3:

Task: Create a function that darkens a color based on a percentage.

Expected Output:

scss

code

@function darken-color($color, $percent) { @return darken($color, $percent); } .btn { background-color: darken-color(#3498db, 10%); }

5. Build a Reusable SCSS UI Kit

Objective:

Build a mini design system using SCSS with variables, mixins, and functions.

Step-by-Step Lab Instructions:

Step 1: Set Up Project Structure

text

code

/project-root |-- /scss | |-- _variables.scss | |-- _mixins.scss | |-- _functions.scss | |-- main.scss

Step 2: Define Variables _variables.scss

scss

 code

$primary-color: #1abc9c; $secondary-color: #2c3e50; $base-padding: 12px; $font-base: 'Roboto', sans-serif;

Step 3: Create Mixins _mixins.scss

scss

 code

@mixin transition($prop...) { transition: $prop 0.3s ease-in-out; } @mixin responsive($breakpoint) { @if $breakpoint == 'tablet' { @media (max-width: 768px) { @content; } } @else if $breakpoint == 'mobile' { @media (max-width: 480px) { @content; } } }

Step 4: Write Functions _functions.scss

scss

code

@function rem($px, $base: 16) { @return ($px / $base) * 1rem; }

Step 5: Use in Main Stylesheet main.scss

scss

 code

@import 'variables', 'mixins', 'functions'; body { font-family: $font-base; padding: $base-padding; } .button { background: $primary-color; color: #fff; padding: rem(14) rem(24); @include transition(all); @include responsive('mobile') { padding: rem(10) rem(20); } }

Expected Outcome: A clean, modular SCSS-based styling system that adapts across devices and reuses components efficiently.

6. Summary

Variables keep your code DRY and make global changes easy.

        

Mixins reduce repetition by encapsulating common patterns.

Functions bring logic to styles and enable dynamic calculations.

SASS improves code organization and maintenance significantly.

7. Assessment Questions

What are the benefits of using mixins over repeating code blocks?

How do SCSS functions differ from mixins?

Create a mixin for a button with custom padding, background color, and text color.

8. Final Exercise

Project Task: Build a responsive card component using:

Variables for spacing and colors.

A mixin for shadows.

A function to convert pixels to rem.

Css Module 42

 

Css Module 42

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Css Module 42

  Module 42 : CSS Nesting with PostCSS – Writing Modular and Maintainable CSS

         

This module introduces the concept of CSS nesting using PostCSS, a powerful tool for transforming CSS with JavaScript. You'll learn how to write modular, maintainable, and cleaner CSS by nesting selectors logically, similar to how it's done in SCSS. The module will also guide you on how to set up PostCSS, structure nested styles efficiently, and avoid common pitfalls.

Learning Objectives:

By the end of this module, learners will be able to:

Understand what CSS nesting is and why it's useful.

Set up PostCSS with the nesting plugin.

Write clean and maintainable nested CSS.

Avoid deep nesting and specificity issues.

Integrate nesting into modular CSS architectures (like BEM or utility-first).

Use PostCSS nesting in real projects.

Section 1: Introduction to CSS Nesting

What is CSS Nesting?

CSS Nesting allows you to nest selectors inside one another, similar to SCSS. This makes it easier to see the relationship between elements and maintain hierarchical styles.

Why Nesting?

Reduces repetition.

Improves readability.

Keeps related styles together.

Helps enforce a component-based structure.

Example (Vanilla CSS vs. Nested CSS)

Without nesting:

css

 code

.card { ... } .card .card-title { ... } .card .card-body { ... } .card .card-footer { ... }

With nesting:

css

code

.card { ... .card-title { ... } .card-body { ... } .card-footer { ... } }

Section 2: Setting Up PostCSS for Nesting

Step-by-step Setup

      

1. Initialize a project:

bash

 code

npm init -y

2. Install required packages:

bash

code

npm install postcss postcss-cli postcss-nesting autoprefixer --save-dev

3. Create a postcss.config.js:

js

code

module.exports = { plugins: [ require('postcss-nesting'), require('autoprefixer') ] }

4. Create a CSS file (src/style.css) using nesting:

css

code

.button { padding: 1rem; background: blue; &:hover { background: darkblue; } span { color: white; } }

5. Build CSS with CLI:

bash code

npx postcss src/style.css -o dist/style.css

Section 3: Writing Modular and Maintainable Nested CSS

Best Practices:

1. Limit Nesting Depth (Max 2-3 levels)

      

  

Too deep nesting increases specificity and becomes hard to read.

css

code

/* Bad */ .card { .header { .title { .icon { color: red; /* Too deep */ } } } }

css

 code

/* Good */ .card { .header { ... } .title { ... } }

2. Use BEM with Nesting

Use nesting to simplify BEM syntax:

css

code

.card { &__title { ... } &__body { ... } }

3. Avoid Nesting Modifiers

Instead of:

css

 code

.card { &.is-active { background: green; } }

Prefer using utility classes or parent selectors where possible.

Section 4: Practical Exercise – Building a Nested Component

Objective:

Create a reusable ProfileCard component using CSS nesting and PostCSS.

HTML:

html

code

<div class="profile-card"> <div class="profile-card__avatar"></div> <div class="profile-card__info"> <h2 class="profile-card__name">Jane Doe</h2> <p class="profile-card__bio">Frontend Developer</p> </div> </div>

Nested CSS:

css

code

.profile-card { display: flex; padding: 1rem; background-color: #fff; &__avatar { width: 80px; height: 80px; background: gray; border-radius: 50%; } &__info { margin-left: 1rem; &__name { font-weight: bold; } &__bio { color: #666; } } }

Refactored (Correct):

css

code

.profile-card { display: flex; padding: 1rem; background-color: #fff; &__avatar { width: 80px; height: 80px; background: gray; border-radius: 50%; } &__info { margin-left: 1rem; } &__name { font-weight: bold; } &__bio { color: #666; } }

Explanation:

Initially, the &__name and &__bio were nested inside &__info, which can complicate the hierarchy and debugging. Flattening them while keeping nesting under control improves maintainability.

Section 5: Exercises

Exercise 1 – Refactor Flat CSS

Take a flat CSS file and refactor it using PostCSS Nesting while following best practices.

        

Exercise 2 – Component Nesting Challenge

Given a UI component structure (e.g., navigation menu), write nested CSS using PostCSS.

Exercise 3 – Analyze and Fix Bad Nesting

Identify issues in a badly nested file and refactor it.

Section 6: Common Pitfalls & Debugging

1. Over-Nesting

Avoid .a .b .c .d .e {} type selectors.

2. Specificity Clashes

Avoid relying on nesting for specificity — use class names and utility-first approaches.

3. Plugin Conflicts

Ensure PostCSS is not using conflicting plugins or misordered plugins.

Section 7: Summary and Best Practices

Nest only when it improves clarity.

Keep nesting depth to 2–3 levels max.

Combine with BEM or utility CSS.

Always lint and auto-format nested styles for consistency.

Assignment (For Students)

Build a full UI component (like a card, navbar, or sidebar) using PostCSS with nesting.

Deliverables:

PostCSS config

Source CSS with nesting

Compiled output

A brief summary of nesting decisions made

Additional Resources

PostCSS Nesting Plugin Docs

MDN Web Docs – CSS Nesting

BEM Methodology

Css Module 41

 

Css Module 41

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Css Module 41

  Module 41 : Understand what CSS Houdini

Objective:

Understand what CSS Houdini is, why it matters, how it extends the capabilities of CSS, and how to use Custom Properties (variables) with Houdini for powerful, dynamic, and performant web styling.

2. What is CSS Houdini?

Definition:

              

CSS Houdini is a set of low-level APIs that allow developers to extend CSS by writing JavaScript that the browser can understand as if it were native CSS.

Why Houdini?

Traditionally, CSS is limited—you can't define new CSS features without waiting for browser vendors.

Houdini bridges the gap between CSS and JavaScript, giving devs the power to create custom styles, layouts, animations, and more.

It allows browsers to parse and render custom styles much faster than traditional JS + DOM manipulation.

3. CSS Houdini APIs Overview

Houdini includes several APIs:

API

Purpose

CSS Typed OM API

Works with CSS values as JS objects instead of strings

Paint Worklet API

Custom drawing with JavaScript (like canvas in CSS)

Layout Worklet API

Create custom layout algorithms

Animation Worklet API

Run animations off the main thread

Properties & Values API

Define and register custom CSS properties

This module focuses on Properties & Values API, essential for understanding Houdini and custom properties.

4. What are Custom Properties?

Custom Properties are variables defined in CSS using --name.

Example:

css

 code

:root { --main-color: #3498db; } .box { background-color: var(--main-color); }

5. Registering Custom Properties with Houdini

       

   

Why Register?

Normally, CSS variables are treated as generic strings. Registering a property gives the browser more information:

Its type (e.g., <color>, <length>)

Default value

Whether it inherits

This improves performance and enables advanced features (like animations, typed values, etc.).

6. How to Register Custom Properties (Step-by-step)

Step 1: Enable Houdini in Browser

Make sure your browser supports Houdini (latest Chrome, Edge, etc.).

Step 2: Use CSS.registerProperty()

javascript

 code

if ('registerProperty' in CSS) { CSS.registerProperty({ name: '--magic-color', syntax: '<color>', inherits: false, initialValue: '#ff00ff' }); }

Now you can use --magic-color in your CSS and it will be treated like a native <color> property.

7. Practical Example: Animating a Custom Color Property

HTML + CSS + JS

html

code

<div class="magic-box"></div> <style> .magic-box { width: 200px; height: 200px; background-color: var(--magic-color, #000); transition: --magic-color 1s ease-in-out; } .magic-box:hover { --magic-color: #00ff00; } </style> <script> if ('registerProperty' in CSS) { CSS.registerProperty({ name: '--magic-color', syntax: '<color>', inherits: false, initialValue: '#ff00ff' }); } </script>

Explanation:

We register --magic-color as a <color> type.

CSS can now animate this property like a native background-color.

On hover, the color transitions smoothly because the browser understands it's a <color>.

8. Custom Progress Bar with Animated Variable

Objective:

Create a progress bar that uses a custom property --progress (type <percentage>) and animates it.

HTML + CSS + JS:

html

 code

<div class="progress-container"> <div class="progress-bar"></div> </div> <style> .progress-container { width: 100%; height: 20px; background: #eee; overflow: hidden; border-radius: 10px; } .progress-bar { height: 100%; background: linear-gradient(to right, #76c7c0, #4b9e9e); transform: scaleX(calc(var(--progress) / 100)); transform-origin: left; transition: --progress 1s ease; } </style> <script> if ('registerProperty' in CSS) { CSS.registerProperty({ name: '--progress', syntax: '<percentage>', inherits: false, initialValue: '0%' }); } const progressBar = document.querySelector('.progress-bar'); // Simulate progress let progress = 0; setInterval(() => { progress += 10; if (progress > 100) progress = 0; progressBar.style.setProperty('--progress', `${progress}%`); }, 1000); </script>

Explanation:

Registers a <percentage> custom property.

Uses it in transform: scaleX() to visually grow the bar.

Transitions are smooth due to typed registration.

9. Exercise

Register a custom property --angle with syntax <angle>.

Apply it to rotate an image on hover with animation.

Make it rotate from 0deg to 45deg.

Hint:

css

code

transform: rotate(var(--angle)); transition: --angle 0.5s;

10. Best Practices

Always check browser support with if ('registerProperty' in CSS) to avoid breaking old browsers.

Use fallback values with var(--prop, fallback).

Register custom properties before using them.

Use typed values to unlock animation capabilities.

11. Summary

       

Feature

Benefit

Custom Properties

Reusable and dynamic styling

Houdini registerProperty

Performance boost and animation support

Typed Syntax

CSS can handle properties natively

Smooth Animations

Registering properties enables browser-native transitions

12. Extension (Optional): Dynamic Themes

Goal:

Create a theme switcher using registered --theme-color property.

Try it:

Define two themes (light/dark)

Use JavaScript to switch --theme-color and see animation.

13. Use Cases

Animated gradients

Advanced theming

Dynamic charts with CSS-driven transitions

Visual effects (like waves, shapes) with Paint API + custom props

14. Final Thoughts

CSS Houdini is the future of dynamic styling. Mastering custom properties with Houdini will give you:

More control

Better performance

Creative freedom beyond standard CSS limitations

Css Module 40

 

Css Module 40 

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Css Module 40

   Module 40 :

1. Introduction to CSS Performance

Why CSS Performance Matters:

CSS may seem lightweight, but inefficient rules and bloated stylesheets can slow down:

Render times (FCP – First Contentful Paint)

Repaints and reflows

Time to Interactive (TTI)

How CSS Affects the Browser:

CSS is render-blocking. Until it's fully downloaded and parsed, the page won't render.

The browser constructs the CSSOM (CSS Object Model) alongside the DOM, and combines them into the Render Tree.

Complex or inefficient styles slow this pipeline.

2. Writing Efficient CSS: 

A. Keep Selectors Short and Simple

Inefficient:

css

 code

html body div.container ul li span.label { color: red; }

Efficient:

css

 code

.label { color: red; }

Explanation:

Deep selectors force the browser to evaluate multiple levels.

Flat selectors target elements directly.

Tip: Use class selectors instead of tag or descendant selectors.

B. Avoid the Universal Selector * and Overly Generic Rules

Example:

css

 code

* { margin: 0; padding: 0; }

While reset styles are useful, * can be costly in large DOMs.

Alternative: Use a scoped reset:

css

 code

body, h1, h2, p, ul, ol { margin: 0; padding: 0; }

C. Use Shorthand Properties

Reduces CSS file size and parsing time.

Instead of:

css

code

margin-top: 10px; margin-right: 10px; margin-bottom: 10px; margin-left: 10px;

Use:

css

code

margin: 10px;

D. Avoid Inline Styles and !important

Inline styles increase HTML size and reduce maintainability.

!important breaks cascading and makes styles harder to override.

E. Minimize Repaints and Reflows

CSS rules like width, height, margin, and position can trigger reflows.

Example: Changing top, left, or width dynamically can reflow the layout.

Optimization:

Use CSS transforms and opacity changes for animations:

css

 code

.element { transform: translateX(100px); opacity: 0.5; }

F. Limit Use of Complex Pseudo-Selectors

Bad:

css

 code

ul li:nth-child(2n+1):hover { background-color: yellow; }

Instead, try using a utility class:

css

code

<li class="odd">...</li>

G. Use Critical CSS

Load only above-the-fold styles in the initial render, defer the rest.

Tools:

Critical by Addy Osmani

webpack plugins for critical CSS

Example:

html

 code

<style> /* Critical CSS inline here */ </style> <link rel="stylesheet" href="main.css" media="print" onload="this.media='all';">

H. Remove Unused CSS

Tools like:

PurgeCSS

UnCSS

Chrome DevTools Coverage tab

These can help eliminate unnecessary rules, especially in large frameworks like Bootstrap.

3. Hands-on Exercises

Exercise 1: Optimize Bloated Selectors

Given:

css

 code

div#main-content .container .article h2.title { color: blue; }

Refactor this to make it more efficient.

Answer:

css

code

.title { color: blue; }

Explanation: The class .title should uniquely identify the element.

Exercise 2: Critical CSS Extraction 

Open a landing page design.

Identify visible content in the viewport.

Copy associated styles into an inline <style> block.

Defer loading the full stylesheet.

Exercise 3: Audit and Optimize a CSS File

Tools:

          

Chrome DevTools > Coverage

PurgeCSS

Steps:

Load a webpage with a large CSS file.

Use Coverage tab to identify unused rules.

Use PurgeCSS to remove them.

Measure file size before and after.

4. Example: Optimizing a Blog Template

Before Optimization:

CSS file size: 230KB

Deep selectors: .blog-post .content > p:first-child

Uses 5 Google Fonts

Animates with top and left

After Optimization:

CSS file size: 80KB

Flat selectors and utility classes

Font stack limited to 1 custom font

Uses transform for animation

Results:

Load time improved by 45%

First Contentful Paint dropped from 1.8s to 1.1s

5. Performance Tools and Testing

Tools to Use:

Lighthouse (Chrome)

WebPageTest

Chrome DevTools – Performance and Coverage tabs

6. Summary of Best Practices

Tip

Why It Helps

Short, flat selectors

Faster evaluation

Use classes over tags or IDs

Easier to manage, better specificity control

Minimize CSS

Reduces download time

Remove unused styles

Cleaner, faster CSSOM

Critical CSS

Improves First Paint

Avoid complex pseudo-classes

Better selector performance

 FormatS

 1:  What happens in the browser           (CSSOM, Render Tree)

CSS as render-blocking resource

  2:  Writing efficient selectors

3:   Exercises: Refactor and audit code

Tools: Lighthouse, PurgeCSS

 4:  Critical CSS & Lazy Loading

CSS for performance in frameworks (Tailwind, Bootstrap)

Homework/Assignment

Project Task:

Take an existing webpage and:

Minimize selector depth

Remove unused rules

Extract critical CSS

Measure performance improvement (before/after)