Select
使用可更改元素初始外观的自定义CSS自定义原生＜select＞。
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默认
自定义＜select＞菜单只需要一个自定义类.form-select即可触发自定义样式。 自定义样式仅限于＜select＞的初始外观，并且由于浏览器的限制，无法修改＜option＞。
<select class="form-select" aria-label="Default select example">
<option selected>Open this select menu</option>
<option value="1">One</option>
<option value="2">Two</option>
<option value="3">Three</option>
</select>尺寸
您也可以从small和large自定义选择中进行选择，以匹配我们类似大小的文本input。
<select class="form-select form-select-lg mb-3" aria-label="Large select example">
<option selected>Open this select menu</option>
<option value="1">One</option>
<option value="2">Two</option>
<option value="3">Three</option>
</select>
<select class="form-select form-select-sm" aria-label="Small select example">
<option selected>Open this select menu</option>
<option value="1">One</option>
<option value="2">Two</option>
<option value="3">Three</option>
</select>还支持multiple属性：
<select class="form-select" multiple aria-label="Multiple select example">
<option selected>Open this select menu</option>
<option value="1">One</option>
<option value="2">Two</option>
<option value="3">Three</option>
</select>与size属性一样：
<select class="form-select" size="3" aria-label="Size 3 select example">
<option selected>Open this select menu</option>
<option value="1">One</option>
<option value="2">Two</option>
<option value="3">Three</option>
</select>Disabled
在select上添加disabled布尔属性，使其显示为灰色，并删除指针事件。
<select class="form-select" aria-label="Disabled select example" disabled>
<option selected>Open this select menu</option>
<option value="1">One</option>
<option value="2">Two</option>
<option value="3">Three</option>
</select>CSS
Sass变量
$form-select-padding-y: $input-padding-y;
$form-select-padding-x: $input-padding-x;
$form-select-font-family: $input-font-family;
$form-select-font-size: $input-font-size;
$form-select-indicator-padding: $form-select-padding-x * 3; // Extra padding for background-image
$form-select-font-weight: $input-font-weight;
$form-select-line-height: $input-line-height;
$form-select-color: $input-color;
$form-select-bg: $input-bg;
$form-select-disabled-color: null;
$form-select-disabled-bg: $input-disabled-bg;
$form-select-disabled-border-color: $input-disabled-border-color;
$form-select-bg-position: right $form-select-padding-x center;
$form-select-bg-size: 16px 12px; // In pixels because image dimensions
$form-select-indicator-color: $gray-800;
$form-select-indicator: url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 16 16'><path fill='none' stroke='#{$form-select-indicator-color}' stroke-linecap='round' stroke-linejoin='round' stroke-width='2' d='m2 5 6 6 6-6'/></svg>");
$form-select-feedback-icon-padding-end: $form-select-padding-x * 2.5 + $form-select-indicator-padding;
$form-select-feedback-icon-position: center right $form-select-indicator-padding;
$form-select-feedback-icon-size: $input-height-inner-half $input-height-inner-half;
$form-select-border-width: $input-border-width;
$form-select-border-color: $input-border-color;
$form-select-border-radius: $input-border-radius;
$form-select-box-shadow: var(--#{$prefix}box-shadow-inset);
$form-select-focus-border-color: $input-focus-border-color;
$form-select-focus-width: $input-focus-width;
$form-select-focus-box-shadow: 0 0 0 $form-select-focus-width $input-btn-focus-color;
$form-select-padding-y-sm: $input-padding-y-sm;
$form-select-padding-x-sm: $input-padding-x-sm;
$form-select-font-size-sm: $input-font-size-sm;
$form-select-border-radius-sm: $input-border-radius-sm;
$form-select-padding-y-lg: $input-padding-y-lg;
$form-select-padding-x-lg: $input-padding-x-lg;
$form-select-font-size-lg: $input-font-size-lg;
$form-select-border-radius-lg: $input-border-radius-lg;
$form-select-transition: $input-transition;