Conditional CSS in React — React Technical Interview Questions & Answers

Conditional CSS in React

Conditional CSS in React

  • Toggle classes from state: className={ok ? 'alert ok' : 'alert bad'}. Or template strings: `btn ${active ? 'btn-on' : ''}`. Libraries: clsx, classnames. Prefer classes over swapping ten inline colors — CSS can animate and theme them.
  • Conditional CSS in React — ok false → alert bad + Failed. Class changes with state.

Technical Interview Tip: className ternary from state.

Code Examples for Conditional CSS in React

Example

// Conditional CSS
export default function Alert({ ok }) {
  return <p className={ok ? "alert ok" : "alert bad"}>{ok ? "Saved" : "Failed"}</p>;
}

Conditional CSS in React — ok false → alert bad + Failed. Class changes with state.

How to Explain Conditional CSS in React to an Interviewer

Explain Conditional CSS as if you are teaching a junior — definition, then one tiny UI.

Ternary className. Or clsx().

Write 5–10 lines that use Conditional CSS and say what the UI does.

Show JSX Say the screen

What mistake do freshers make with Conditional CSS?

Prefer classes over inline rainbows.