示例 2
====

这是解释如何构建自定义表单控件的第二个示例。

使用 JS
-----

### HTML


```html
<form class="no-widget">
  <select name="myFruit">
    <option>Cherry</option>
    <option>Lemon</option>
    <option>Banana</option>
    <option>Strawberry</option>
    <option>Apple</option>
  </select>

  <div class="select">
    <span class="value">Cherry</span>
    <ul class="optList hidden">
      <li class="option">Cherry</li>
      <li class="option">Lemon</li>
      <li class="option">Banana</li>
      <li class="option">Strawberry</li>
      <li class="option">Apple</li>
    </ul>
  </div>
</form>
```

### CSS


```css
.widget select,
.no-widget .select {
  position: absolute;
  left: -5000em;
  height: 0;
  overflow: hidden;
}

/\*--------- \*/
/\* 所需的样式 \*/
/\* -------- \*/

.select {
  position: relative;
  display: inline-block;
}

.select.active,
.select:focus {
  box-shadow: 0 0 3px 1px #227755;
  outline: none;
}

.select .optList {
  position: absolute;
  top: 100%;
  left: 0;
}

.select .optList.hidden {
  max-height: 0;
  visibility: hidden;
}

/\* ------- \*/
/\* 美化样式 \*/
/\* ------- \*/

.select {
  font-size: 0.625em; /\* 10px \*/
  font-family: Verdana, Arial, sans-serif;

  box-sizing: border-box;

  padding: 0.1em 2.5em 0.2em 0.5em; /\* 1px 25px 2px 5px \*/
  width: 10em; /\* 100px \*/

  border: 0.2em solid #000; /\* 2px \*/
  border-radius: 0.4em; /\* 4px \*/

  box-shadow: 0 0.1em 0.2em rgba(0, 0, 0, 0.45); /\* 0 1px 2px \*/

  background: #f0f0f0;
  background: linear-gradient(0deg, #e3e3e3, #fcfcfc 50%, #f0f0f0);
}

.select .value {
  display: inline-block;
  width: 100%;
  overflow: hidden;

  white-space: nowrap;
  text-overflow: ellipsis;
  vertical-align: top;
}

.select::after {
  content: "▼";
  position: absolute;
  z-index: 1;
  height: 100%;
  width: 2em; /\* 20px \*/
  top: 0;
  right: 0;

  padding-top: 0.1em;

  box-sizing: border-box;

  text-align: center;

  border-left: 0.2em solid #000;
  border-radius: 0 0.1em 0.1em 0;

  background-color: #000;
  color: #fff;
}

.select .optList {
  z-index: 2;

  list-style: none;
  margin: 0;
  padding: 0;

  background: #f0f0f0;
  border: 0.2em solid #000;
  border-top-width: 0.1em;
  border-radius: 0 0 0.4em 0.4em;

  box-shadow: 0 0.2em 0.4em rgba(0, 0, 0, 0.4);

  box-sizing: border-box;

  min-width: 100%;
  max-height: 10em; /\* 100px \*/
  overflow-y: auto;
  overflow-x: hidden;
}

.select .option {
  padding: 0.2em 0.3em;
}

.select .highlight {
  background: #000;
  color: #ffffff;
}
```

### JavaScript


```js
window.addEventListener("load", () => {
  const form = document.querySelector("form");

  form.classList.remove("no-widget");
  form.classList.add("widget");
});
```

### 结果

不使用 JS
------

### HTML


```html
<form class="no-widget">
  <select name="myFruit">
    <option>Cherry</option>
    <option>Lemon</option>
    <option>Banana</option>
    <option>Strawberry</option>
    <option>Apple</option>
  </select>

  <div class="select">
    <span class="value">Cherry</span>
    <ul class="optList hidden">
      <li class="option">Cherry</li>
      <li class="option">Lemon</li>
      <li class="option">Banana</li>
      <li class="option">Strawberry</li>
      <li class="option">Apple</li>
    </ul>
  </div>
</form>
```

### CSS


```css
.widget select,
.no-widget .select {
  position: absolute;
  left: -5000em;
  height: 0;
  overflow: hidden;
}
```

### 结果