personal-site/components/ThemeToggle.js

import { useEffect, useState } from 'react';
import Icon from './Icon';

export default function ThemeToggle() {
  const [theme, setTheme] = useState(null);

  useEffect(() => {
    setTheme(document.documentElement.dataset.theme || 'light');
  }, []);

  const toggle = () => {
    const next = theme === 'dark' ? 'light' : 'dark';
    document.documentElement.dataset.theme = next;
    try {
      localStorage.setItem('theme', next);
    } catch (e) {}
    setTheme(next);
  };

  return (
    <button
      type="button"
      className="icon-button"
      onClick={toggle}
      aria-label={`Switch to ${theme === 'dark' ? 'light' : 'dark'} theme`}
    >
      <Icon name={theme === 'dark' ? 'sun' : 'moon'} />
    </button>
  );
}