只需保存并从localStorage获取它，然后将其应用于正在使用文档效果
例如：

function Theme() {

  useEffect(()=>{
    const mode = localStorage.getItem("mode");
  
  
     if(mode){
       document.documentElement.classList.add("dark");
    
     }

   },[])
  
  const toggleMode = (mode) => {
    if (mode === "add") {
      document.documentElement.classList.add("dark");
      localStorage.setItem('mode','dark')
    } else {
      document.documentElement.classList.remove("dark");
      localStorage.removeItem('mode')
      
    }
  };
  return (
    <div className="theme_toggle">
      <div className="day_mode flex items-center" onClick={() => toggleMode("add")} >
        <Image src="/dark.svg" width="20" height="20" alt="night_mood" />
      </div>
      <div className="night_mode flex items-center" onClick={() => toggleMode("remove")} >
        <Image src="/day_white.svg" width="20" height="20" alt="day_mood" />
      </div>
    </div>
  )
}

export default Theme