style(common.css): 更新头部下拉面板弹出动画

public/themes/dist_static/static/css/common.css

@@ -32,6 +32,10 @@
   --duration-normal: 0.3s;       /* 变换/位移/透明度/展开收起 */
   --duration-slow: 0.4s;         /* 轮播/大幅位移 */
   --easing: ease;                /* 缓动函数 */
+
+  --nav--dropdown-duration: 300ms;
+  --ease-expo-out: cubic-bezier(0.16, 1, 0.3, 1);
+  --nav--dropdown-open-duration: 600ms;
 }/* max-width 从大到小写 *//* 1680–1919：比 1920 稿略窄，边距收到 100 */@media (max-width: 1919px) {
   :root {
     --p-x: 100Px;
@@ -1307,14 +1311,16 @@ body {
   right: 0;
   top: 100%;
   z-index: 2;
+  /* 展开收起动画 */
   display: grid;
   grid-template-rows: 0fr;
-  max-height: calc(100dvh - var(--header-h));
   visibility: hidden;
+  opacity: 0;
+  transition: grid-template-rows var(--nav--dropdown-duration) var(--ease-expo-out), visibility 0s var(--nav--dropdown-duration), opacity var(--nav--dropdown-duration) var(--ease-expo-out);
+  max-height: calc(100dvh - var(--header-h));
   background: var(--color-white);
   border-top: 1px solid rgb(223, 224, 226);
   box-shadow: 0 1.5rem 3rem rgba(46, 53, 58, 0.08);
-  transition: grid-template-rows 0.5s var(--easing);
 }.nav-mega__inner {
   overflow: auto;
   min-height: 0;
@@ -1617,6 +1623,8 @@ body {
 }.site-header__nav-item:hover .nav-mega {
   grid-template-rows: 1fr;
   visibility: visible;
+  opacity: 1;
+  transition: grid-template-rows var(--nav--dropdown-open-duration) var(--ease-expo-out), visibility 0s 0s, opacity var(--nav--dropdown-duration) var(--ease-expo-out);
 }.site-header__nav-item:hover .site-header__nav-link {
   color: var(--color-primary);
 }.site-header__nav-item:hover .site-header__chevron {