style(ui): 调整下拉菜单样式和下载链接宽度

- 为Mac下载链接添加100%宽度样式
- 将下拉菜单最小宽度从200px调整为156px
- 优化下拉菜单视觉效果

_config/css/styles.css

@@ -282,7 +282,7 @@ background-color: #ccc;
   top: 100%;
   left: 0;
   margin-top: 8px;
-  min-width: 200px;
+  min-width: 156px;
   background: #fff;
   border: 2px solid var(--theme-color);
   border-radius: 5px;

_coverpage.md

@@ -101,8 +101,8 @@
       <div class="dropdown">
         <a class="dropdown-toggle" href="javascript:void(0)"><span>Mac 下载</span></a>
         <div class="dropdown-menu">
-          <a href="./_media/package/mac-luckday-screen.zip" rel="noopener" target="_blank"><span>Mac (Intel 芯片)</span></a>
-          <a href="./_media/package/mac-arm64-luckday-screen.zip" rel="noopener" target="_blank"><span>Mac (Apple 芯片)</span></a>
+          <a href="./_media/package/mac-luckday-screen.zip" rel="noopener" target="_blank" style="width: 100%"><span>Mac (Intel 芯片)</span></a>
+          <a href="./_media/package/mac-arm64-luckday-screen.zip" rel="noopener" target="_blank" style="width: 100%"><span>Mac (Apple 芯片)</span></a>
         </div>
       </div>
     </div>