Fill the space between lines to highlight the greater-than and less-than differences over time.
Tutorials and Guides
How I Made That: Animated Difference Charts in R
A combination of a bivariate area chart, animation, and a population pyramid, with a sprinkling of detail and annotation.
How I Made That: Searchable Time Series Chart
When there are too many options or categories, it can be helpful to make the data searchable.