用javascr ipt实现当鼠标指向主菜单时，主菜单中的菜单项会以奇偶的形式从左右两边向中间移动，并将透明的菜单项转为不透明状态-Using javascr ipt when the mouse to point to the main menu, the menu item in the main menu to the form of parity from the left and right sides to move toward the middle, and the transparent menu items into opaque state