前言

app.js

import React, {useState} from 'react';
import './App.css';

const App = () => {

    const [redBorder, setRedBorder] = useState(true);

    // const pStyle = {
    //     color: 'red',
    //     backgroundColor: '#bfa',
    //     border: redBorder ? "red solid 1px" : "blue solid 1px"
    // };

    const clickHandler = () => {
        setRedBorder(false);
    };

    return (
        <div>
            <p className={`p1 ${redBorder?'':'blueBorder'}`}>我是一个段落</p>
            <button onClick={clickHandler}>点我一下</button>
        </div>
    );
};

export default App;

app.css

.p1{
    color: red;
    background-color: #bfa;
    border: 1px red solid;
}

.blueBorder{
    border: 1px blue solid;
}