如何使横坐标(即网格线y=0)在ggplot2中显得更黑或更粗?

I have a line graph with some points with positive value, and others with negative value (I am plotting odds ratios). I would like to make the y=0 grid line appear darker or bolder so as to make the visuals more apparent. How can I do this with ggplot2?I have a line graph with some points with posit