Javascript 更改宽度并将其保存到localstorage

const cek = document.getElementById("fxd"),
      bbx = document.getElementById("box");

// check if localStorage . if yes set width
const checkWidthSet = localStorage.getItem('widthSet')

if (checkWidthSet === "true" ) {  
  bbx.classList.toggle("fixed");
}

cek.addEventListener("change", () => {
  const w = localStorage.getItem('widthSet');    
  if (w === "true") 
  {    
    localStorage.setItem('widthSet', false)      
  } else {        
    localStorage.setItem('widthSet', true)    
  }
  bbx.classList.toggle("fixed");  
});

*,
*::before,
*::after {
    box-sizing: border-box;
}

body {
    padding: 0;
    margin: 0;
    font-family: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans", "Liberation Sans", sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji";
    background-color: #16202c;
}

.warpper {
    width: 500px;
    text-align: center;
}

.box {
    display: block;
    width: 100%;
    height: 250px;
    background-color: #223444;
    margin: 0 auto;
    transition: .6s easier;
}

.fixed {
    max-width: 350px;
    transition: .6s easier;
}

.chkb {
    display: flex;
    justify-content: center;
    align-items: center;
    width: 100%;
    height: 100vh;
}

.check {
    position: relative;
    width: 40px;
    height: 15px;
    background-color: #223444;
    outline: none;
    -webkit-appearance: none;
    border-radius: 20px;
    cursor: pointer;
    box-shadow: inset 0 0 5px rgba(0, 0, 0, .9);
    //*border: 1px solid #111923;*//
}

.check:checked {
    background-color: #1e69de;
}

.check:before {
    background-color: #0F121E;
    content: "";
    position: absolute;
    width: 15px;
    height: 15px;
    border-radius: 50%;
    left: 0;
    top: 0;
    transform: scale(1.4);
    transition: .3s;
    box-shadow: 0 0 5px rgba(0, 0, 0, .6);
}

.check:checked:before {
    left: 22px;
    background-color: #1e69de;
}

.head {
    border: 1px solid #223444;
    padding: 10px 7px;
    display: flex;
    justify-content: space-between;
    margin-bottom: 5px;
    color: #1e69de;
}

<div class="chkb">
        <div class="warpper">
            <div class="head">
                <div class="">Change Width</div>
                <input type="checkbox" id="fxd" class="check" name="theme" >
                <!--<button type="button" class="btn">Change</button>-->
            </div>
            <div id="box" class="box"></div>
        </div>
    </div>