下拉列表（Select）
使用重置的CSS，重定義原生的下拉列表外觀。
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默認
自定義code><select>菜單只需要一個自定義類.form-select就可以觸發自定義樣式。自定義樣式僅限于select的初始外觀，并且由于瀏覽器的限制，無法修改<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>大小
Y您也可以選擇從小型和大型定制選擇，以匹配我們同樣大小的文本輸入。
<select class="form-select form-select-lg mb-3" aria-label=".form-select-lg 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=".form-select-sm example">
<option selected>Open this select menu</option>
<option value="1">One</option>
<option value="2">Two</option>
<option value="3">Three</option>
</select>還支持多文件屬性multiple ,按住Ctrl鍵，可以一次選擇多個選項
<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>支持大小屬性 size :
<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>禁用
在select上添加 disabled屬性，使其顯示為灰色，并刪除指針事件。
<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>Sass
Variables
$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: $gray-200;
$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 5l6 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: $border-radius;
$form-select-box-shadow: $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-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;