Javascript：第一个下拉框工作，而另一个不工作。代码是一样的

I am wanting to have nine drop-down boxes but currently only have two. The problem is that only one of them are working yet the code for both of them are the same apart from the obvious changes in ID's for different parts of the HTML. When i click the first one ("mid_side_button") it works perfectly and displays the content that has been created using CSS. When i click the other button ("right_side_button"), it doesn't do anything.I am wanting to have nine drop-down boxes but c