Educational

CSS Basics with React

—

by

Saim Khalid
in

Styling is a crucial part of every React application. It helps you define how your components look, how the user interacts with them, and how your overall UI feels. In React, CSS plays a vital role in bringing components to life. This post explains how to include standard CSS files in a React project, organize global versus component-specific styles, and follow best practices for a scalable folder structure.

Introduction

React is a component-based library, meaning your UI is divided into small, reusable building blocks. Each component can have its own styles, or share styles across the application. Understanding how to manage and structure CSS efficiently ensures that your project remains organized and maintainable as it grows.

In traditional HTML and CSS projects, styles are applied globally using <link> tags or inline style attributes. However, in React, you have several structured ways to include and manage your CSS.

Let’s explore the basics of linking and using stylesheets in React.

Including CSS in React

In React applications (especially those created with Create React App, Vite, or Next.js), you can include CSS in multiple ways. The most fundamental method is by importing CSS files directly into your components or global entry points.

Example 1: Importing a Global CSS File

In your React app, you usually have a global stylesheet such as index.css or App.css.

File: index.js

import React from "react";
import ReactDOM from "react-dom/client";
import "./index.css";
import App from "./App";

const root = ReactDOM.createRoot(document.getElementById("root"));
root.render(<App />);

File: index.css

body {
  margin: 0;
  font-family: Arial, Helvetica, sans-serif;
  background-color: #f8f8f8;
}

Here, the index.css file contains styles that apply globally to your application, such as the body background or font family.

Example 2: Importing CSS in a Component

Every React component can have its own CSS file. This approach helps to isolate styles and makes your components reusable.

File: App.js

import React from "react";
import "./App.css";

function App() {
  return (

&lt;div className="app-container"&gt;
  &lt;h1&gt;Welcome to React Styling&lt;/h1&gt;
  &lt;p&gt;This is a simple example of CSS in React.&lt;/p&gt;
&lt;/div&gt;
  );
}

export default App;

File: App.css

.app-container {
  padding: 20px;
  text-align: center;
  background-color: white;
  border-radius: 10px;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
}

h1 {
  color: #333;
}

p {
  color: #666;
}

In this example, the App.css file defines component-specific styles, and the App.js imports that file directly.

Organizing Global vs Component-Specific Styles

In React, you often need to separate global styles (like typography, layout, and theme colors) from component-specific styles (unique to each component).

Global Styles

Global styles affect the entire application. They are generally placed in files such as index.css or globals.css.

Examples of what goes into global styles:

  • CSS resets or normalize rules
  • Font imports
  • Global layout (like container widths, grid setup)
  • Theme variables (colors, font sizes, spacing)

File: globals.css

:root {
  --primary-color: #007bff;
  --secondary-color: #6c757d;
  --background-color: #f5f5f5;
  --font-family: "Roboto", sans-serif;
}

body {
  margin: 0;
  background-color: var(--background-color);
  font-family: var(--font-family);
  color: #333;
}

These variables can then be reused across all components.

Component-Specific Styles

Each component can have a dedicated CSS file to avoid clutter and naming conflicts.

For example, if you have a Button component, you can store its styles in Button.css.

File: Button.js

import React from "react";
import "./Button.css";

function Button({ label }) {
  return <button className="primary-btn">{label}</button>;
}

export default Button;

File: Button.css

.primary-btn {
  background-color: var(--primary-color);
  color: white;
  padding: 10px 20px;
  border: none;
  border-radius: 5px;
  cursor: pointer;
  transition: background-color 0.2s ease-in-out;
}

.primary-btn:hover {
  background-color: #0056b3;
}

This method ensures that the button styles are isolated from other components.

Organizing CSS Folder Structure

As your React project grows, having a well-structured CSS folder is essential for scalability and maintainability.

Here’s a commonly used structure:

src/
│
├── index.js
├── index.css
├── App.js
├── App.css
│
├── components/
│   ├── Button/
│   │   ├── Button.js
│   │   └── Button.css
│   ├── Header/
│   │   ├── Header.js
│   │   └── Header.css
│   ├── Footer/
│   │   ├── Footer.js
│   │   └── Footer.css
│
└── styles/

├── globals.css
├── variables.css
├── layout.css

Explanation of Folders

  • components/: Each subfolder contains a component and its associated CSS file.
  • styles/: Contains global and shared styles, such as color variables, typography, and layout rules.
  • App.css: Handles top-level application styles.

Using CSS Variables

CSS variables allow you to maintain consistent design values across your React app.

File: variables.css

:root {
  --primary-color: #4caf50;
  --danger-color: #f44336;
  --font-size-large: 1.2rem;
  --spacing-small: 8px;
}

Using Variables in a Component CSS

.card {
  background-color: white;
  border: 1px solid #ddd;
  border-radius: 10px;
  padding: var(--spacing-small);
  color: var(--primary-color);
}

By defining and using variables this way, updating design themes becomes much easier.

Avoiding Style Conflicts

When working with multiple developers or large projects, class name collisions are common if you use standard CSS files. To prevent that, follow these tips:

  1. Use a Naming Convention
    Adopt a clear naming pattern, like BEM (Block Element Modifier).
    Example: .card {} .card__header {} .card__footer--highlighted {}
  2. Component Scoping
    Keep CSS files next to their components and avoid using generic names.
  3. Use a Prefix
    Add component prefixes to class names for better isolation.
    Example: .btn-primary {} .btn-secondary {}

Linking External CSS Libraries

You can also use third-party CSS libraries in React.

For example, linking Bootstrap in your React project:

Method 1: Import via npm

Install Bootstrap using npm:

npm install bootstrap

Then import it in your index.js:

import "bootstrap/dist/css/bootstrap.min.css";

You can now use Bootstrap classes directly:

<button className="btn btn-primary">Click Me</button>

Method 2: Linking in HTML

Alternatively, you can add it to your public/index.html:

<link
  rel="stylesheet"
  href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css"
/>

Both methods work well, but using npm imports keeps everything bundled.

Handling Media Queries in React CSS

Media queries can be used directly in your CSS files to make components responsive.

Example:

.container {
  width: 90%;
  margin: 0 auto;
}

@media (min-width: 768px) {
  .container {

width: 70%;
  }
}

This ensures your React components adapt to different screen sizes.

Best Practices for Scalable CSS in React

When building larger applications, a consistent CSS approach becomes vital. Here are some best practices:

1. Keep CSS Modular

Each component should have its own CSS file. This helps prevent style leakage and makes debugging easier.

2. Use a Naming Convention

Adopt consistent naming, like BEM or camelCase, across all CSS files.

3. Centralize Global Styles

Place all global rules and variables in the /styles directory.

4. Avoid Inline Styles for Complex Design

Inline styles are useful for dynamic values but can clutter JSX and reduce reusability.

5. Optimize for Performance

Avoid unnecessary re-renders due to inline style objects and use minified CSS in production.

6. Use Comments and Documentation

Document CSS rules that may not be obvious. This helps future developers understand why certain styles exist.

Example Project Structure with CSS

Let’s visualize a more complete example:

src/
│
├── App.js
├── App.css
├── index.js
├── index.css
│
├── styles/
│   ├── globals.css
│   ├── variables.css
│   ├── typography.css
│
├── components/
│   ├── Navbar/
│   │   ├── Navbar.js
│   │   └── Navbar.css
│   ├── Card/
│   │   ├── Card.js
│   │   └── Card.css
│   └── Button/
│       ├── Button.js
│       └── Button.css
│
└── assets/

├── images/
└── fonts/

This type of organization helps keep global and local styles neatly separated.

Combining CSS with JavaScript Logic

Sometimes, you might want to toggle styles dynamically based on state or props.

Example:

import React, { useState } from "react";
import "./Button.css";

function ToggleButton() {
  const [active, setActive] = useState(false);

  return (

&lt;button
  className={active ? "btn-active" : "btn-inactive"}
  onClick={() =&gt; setActive(!active)}
&gt;
  {active ? "Active" : "Inactive"}
&lt;/button&gt;
  );
}

export default ToggleButton;

File: Button.css

.btn-active {
  background-color: var(--primary-color);
  color: white;
}

.btn-inactive {
  background-color: #ccc;
  color: black;
}

This shows how JavaScript logic and CSS can work together for interactive design.

Managing Large-Scale Styling

As your project scales, maintaining CSS can become difficult. While CSS Modules and Styled Components are advanced alternatives, even basic CSS can be scalable with discipline.

Tips for large projects:

  • Break CSS into small, logical chunks.
  • Avoid using IDs in CSS selectors.
  • Create a reusable pattern library or design system.
  • Use CSS variables and global themes.
  • Periodically clean unused classes and files.

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