工具提示在我的pygal条形图中不起作用？

Following my python book, I made a bar graph using pygal. I rendered the information to an .svg file and opened it up in my web browser. My book says that the plot is interactive and will show you the value of each bar if you hover over it. However, whenever I hover my mouse over the graph, nothing happens. I am using a mac and google chrome to view the file.Following my python book, I made a bar graph us