<!-- 組件：下拉菜單 --><div class="dropdown"> <!-- 觸發按鈕 --> <button class="btn btn-default dropdown-toggle" type="button" data-toggle="dropdown"> Dropdown <span class="caret"></span> </button> <!-- 下拉菜單 --> <ul class="dropdown-menu"> <li><a href="#">Action</a></li> <li><a href="#">Another action</a></li> <li><a href="#">Something else here</a></li> </ul></div>

// Dropdown arrow/caret.caret { display: inline-block; width: 0; height: 0; margin-left: 2px; vertical-align: middle; border-top: @caret-width-base dashed; border-top: @caret-width-base solid ~"/9"; // IE8 border-right: @caret-width-base solid transparent; border-left: @caret-width-base solid transparent;}// The dropdown wrapper (div).dropup,.dropdown { position: relative; // 父元素相對定位}// Prevent the focus on the dropdown toggle when closing dropdowns.dropdown-toggle:focus { outline: 0;}// The dropdown menu (ul).dropdown-menu { position: absolute; //子元素絕對定位 top: 100%; // 下拉菜單緊貼父元素下邊沿 left: 0; z-index: @zindex-dropdown; display: none; //默認隱藏，當觸發按鈕顯示(display:block) float: left; min-width: 160px; padding: 5px 0; margin: 2px 0 0; // override default ul list-style: none; font-size: @font-size-base; text-align: left;  background-color: @dropdown-bg; border: 1px solid @dropdown-fallback-border; // IE8 fallback border: 1px solid @dropdown-border; border-radius: @border-radius-base; .box-shadow(0 6px 12px rgba(0,0,0,.175)); background-clip: padding-box; // Aligns the dropdown menu to right &.pull-right { right: 0; left: auto; } // 高度為1px的水平分隔線 .divider { .nav-divider(@dropdown-divider-bg); } // Links within the dropdown menu > li > a { display: block; padding: 3px 20px; clear: both; font-weight: normal; line-height: @line-height-base; color: @dropdown-link-color; white-space: nowrap; // 防止鏈接換行 }}// Hover/Focus state.dropdown-menu > li > a { &:hover, &:focus { text-decoration: none; color: @dropdown-link-hover-color; background-color: @dropdown-link-hover-bg; }}// Active state.dropdown-menu > .active > a { &, &:hover, &:focus { color: @dropdown-link-active-color; text-decoration: none; outline: 0; background-color: @dropdown-link-active-bg; }}// 顯示下拉菜單.open {  > .dropdown-menu { display: block; // 顯示 } // Remove the outline when :focus is triggered > a { outline: 0; }}// Menu positioning.dropdown-menu-right { left: auto; // Reset the default from `.dropdown-menu` right: 0;}// `.pull-right` nav component..dropdown-menu-left { left: 0; right: auto;}// Dropdown section headers.dropdown-header { display: block; padding: 3px 20px; font-size: @font-size-small; line-height: @line-height-base; color: @dropdown-header-color; white-space: nowrap; // as with > li > a}// 非下拉菜單區域.dropdown-backdrop { position: fixed; left: 0; right: 0; bottom: 0; top: 0; z-index: (@zindex-dropdown - 10); //確保點擊下拉菜單時，不會關閉下拉菜單}// Right aligned dropdowns.pull-right > .dropdown-menu { right: 0; left: auto;}// Allow for dropdowns to go bottom up (aka, dropup-menu)//// Just add .dropup after the standard .dropdown class and you're set, bro.// TODO: abstract this so that the navbar fixed styles are not placed here?.dropup,.navbar-fixed-bottom .dropdown { // Reverse the caret .caret { border-top: 0; border-bottom: @caret-width-base dashed; border-bottom: @caret-width-base solid ~"/9"; // IE8 content: ""; } // Different positioning for bottom up menu .dropdown-menu { top: auto; bottom: 100%; margin-bottom: 2px; }}// Component alignment//// Reiterate per navbar.less and the modified component alignment there.@media (min-width: @grid-float-breakpoint) { .navbar-right { .dropdown-menu {  .dropdown-menu-right(); } // Necessary for overrides of the default right aligned menu. // Will remove come v4 in all likelihood. .dropdown-menu-left {  .dropdown-menu-left(); } }}

/* ======================================================================== * Bootstrap: dropdown.js v3.3.6 * http://getbootstrap.com/javascript/#dropdowns * ======================================================================== * Copyright 2011-2016 Twitter, Inc. * Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE) * ======================================================================== */+function ($) { 'use strict'; // DROPDOWN CLASS DEFINITION // ========================= var backdrop = '.dropdown-backdrop' var toggle = '[data-toggle="dropdown"]' var Dropdown = function (element) { $(element).on('click.bs.dropdown', this.toggle) } Dropdown.VERSION = '3.3.6' function getParent($this) { var selector = $this.attr('data-target') if (!selector) {  selector = $this.attr('href')  selector = selector && /#[A-Za-z]/.test(selector) && selector.replace(/.*(?=#[^/s]*$)/, '') // strip for ie7 } var $parent = selector && $(selector) return $parent && $parent.length ? $parent : $this.parent() } function clearMenus(e) { if (e && e.which === 3) return $(backdrop).remove() $(toggle).each(function () {  var $this   = $(this)  var $parent  = getParent($this)  var relatedTarget = { relatedTarget: this }  if (!$parent.hasClass('open')) return  if (e && e.type == 'click' && /input|textarea/i.test(e.target.tagName) && $.contains($parent[0], e.target)) return  $parent.trigger(e = $.Event('hide.bs.dropdown', relatedTarget))  if (e.isDefaultPrevented()) return  $this.attr('aria-expanded', 'false')  $parent.removeClass('open').trigger($.Event('hidden.bs.dropdown', relatedTarget)) }) } Dropdown.prototype.toggle = function (e) { var $this = $(this) if ($this.is('.disabled, :disabled')) return var $parent = getParent($this) var isActive = $parent.hasClass('open') clearMenus() if (!isActive) {  if ('ontouchstart' in document.documentElement && !$parent.closest('.navbar-nav').length) {  // if mobile we use a backdrop because click events don't delegate  $(document.createElement('div'))   .addClass('dropdown-backdrop')   .insertAfter($(this))   .on('click', clearMenus)  }  var relatedTarget = { relatedTarget: this }  $parent.trigger(e = $.Event('show.bs.dropdown', relatedTarget))  if (e.isDefaultPrevented()) return  $this  .trigger('focus')  .attr('aria-expanded', 'true')  $parent  .toggleClass('open')  .trigger($.Event('shown.bs.dropdown', relatedTarget)) } return false } Dropdown.prototype.keydown = function (e) { if (!/(38|40|27|32)/.test(e.which) || /input|textarea/i.test(e.target.tagName)) return var $this = $(this) e.preventDefault() e.stopPropagation() if ($this.is('.disabled, :disabled')) return var $parent = getParent($this) var isActive = $parent.hasClass('open') if (!isActive && e.which != 27 || isActive && e.which == 27) {  if (e.which == 27) $parent.find(toggle).trigger('focus')  return $this.trigger('click') } var desc = ' li:not(.disabled):visible a' var $items = $parent.find('.dropdown-menu' + desc) if (!$items.length) return var index = $items.index(e.target) if (e.which == 38 && index > 0)     index--   // up if (e.which == 40 && index < $items.length - 1) index++   // down if (!~index)         index = 0 $items.eq(index).trigger('focus') } // DROPDOWN PLUGIN DEFINITION // ========================== function Plugin(option) { return this.each(function () {  var $this = $(this)  var data = $this.data('bs.dropdown')  if (!data) $this.data('bs.dropdown', (data = new Dropdown(this)))  if (typeof option == 'string') data[option].call($this) }) } var old = $.fn.dropdown $.fn.dropdown    = Plugin $.fn.dropdown.Constructor = Dropdown // DROPDOWN NO CONFLICT // ==================== $.fn.dropdown.noConflict = function () { $.fn.dropdown = old return this } // APPLY TO STANDARD DROPDOWN ELEMENTS // =================================== $(document) .on('click.bs.dropdown.data-api', clearMenus) .on('click.bs.dropdown.data-api', '.dropdown form', function (e) { e.stopPropagation() }) .on('click.bs.dropdown.data-api', toggle, Dropdown.prototype.toggle) .on('keydown.bs.dropdown.data-api', toggle, Dropdown.prototype.keydown) .on('keydown.bs.dropdown.data-api', '.dropdown-menu', Dropdown.prototype.keydown)}(jQuery);