If you would like grid lines that go across the graph, you can make the following call to svg_1d_plot:

my_plot.x_major_grid_on(true)
       .x_minor_grid_on(true);

To style it, you would use the following calls:

my_plot.x_major_grid_color(lightgray)
       .x_minor_grid_color(whitesmoke);

This will produce something like the following image:

For an alternate way to display a regular axis, you can use an external style:

my_plot.x_external_style_on(true);

The axis is still styled using the normal methods. The following is an example of the style that you can produce with this.