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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallUse className in JSX to connect an element to an ordinary CSS class, then define that class in a stylesheet. Use React’s style prop when a style value comes from JavaScript data, and use conditional class names when a component’s state changes which reusable styles apply. How the CSS file gets loaded depends on your project’s build tool or framework.
Connect a CSS class to a React element
In JSX, write className rather than the HTML attribute class. Its value is the name of a CSS class, which you define in a stylesheet as usual.
// Card.jsx
import './Card.css';
export default function Card() {
return (
<article className="card">
<h2 className="card__title">Profile</h2>
</article>
);
}/* Card.css */
.card {
padding: 1rem;
border: 1px solid #ccc;
border-radius: 0.5rem;
}
.card__title {
margin: 0;
color: #222;
}import './Card.css'; is a common bundler convention, not a universal React rule. React does not prescribe how CSS files are loaded: use the CSS-loading approach supported by your build tool or framework. In a simple HTML project, a stylesheet can instead be connected with a <link> element.
Choose classes or inline styles
Prefer CSS classes for values known ahead of time and styles you want to reuse, including rules that use selectors, pseudo-classes, or media queries. React recommends using the style attribute when styles depend on JavaScript variables.
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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteThe style prop takes a JavaScript object. Property names use camelCase, and numeric values are generally rendered with px unless the CSS property is unitless.
function Avatar({ size }) {
return (
<img
className="avatar"
style={{ width: size, height: size }}
src="/avatar.png"
alt=""
/>
);
}Here the class handles reusable avatar styling while the dimensions vary with the size value. For example, backgroundColor is the JavaScript style-property spelling corresponding to CSS background-color.
Apply styles conditionally
Build the className string with ordinary JavaScript. Keep the base class and add a modifier class when its condition is true.
import './Card.css';
export default function Card({ selected }) {
return (
<article className={selected ? 'card card--selected' : 'card'}>
<h2 className="card__title">Profile</h2>
</article>
);
}.card--selected {
border-color: royalblue;
background: #f3f7ff;
}For more involved combinations, a helper such as classnames is optional; it can make class composition easier to read, but is not required by React.
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What changes with React 19 stylesheet elements?
React 19 supports rendering stylesheet <link> and <style> elements as part of the rendered tree. A stylesheet link can use the precedence prop to let React manage stylesheet ordering in the document head; identical linked stylesheets can be deduplicated. This is a React 19 capability, not a requirement for using CSS in React. Whether it fits your app depends on its rendering architecture and framework.
Type an inline style object in TypeScript
Use React.CSSProperties to type an inline style object when you need to declare one separately.
import type { CSSProperties } from 'react';
const avatarStyle: CSSProperties = {
width: 48,
height: 48,
};Then pass it to an element with style={avatarStyle}. Keep values that are fixed and reusable in CSS where practical; reserve the object for values driven by JavaScript.
Troubleshoot styles that do not appear
- The class has no effect: Check that the JSX uses
className, that its value matches the selector spelling in the CSS file, and that the stylesheet is actually loaded. - The stylesheet import fails: Confirm that your build tool or framework supports importing CSS from that location, and follow its stylesheet-loading instructions. A CSS import is not built into JSX as a universal loading mechanism.
- An inline value looks wrong: Check camelCase property names and remember that numeric values normally gain a
pxunit unless the property is unitless. Use an explicit string when a different unit is needed, such aswidth: '50%'. - A conditional appearance never changes: Verify the condition’s value and inspect the resulting class string. Ensure the modifier selector is defined in a stylesheet that is loaded.
Capture a rendered page for review
If you need a screenshot of a deployed React page, first make the page reachable at a URL. A screenshot service cannot replace the CSS setup above; it captures the result after the browser renders the page.
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