I tried to understand which classes were involved in the style for the axis but It didn't help me at all.
I didn't find the right class to add a margin between the axis and the text.
Could you suggest me something about it ?
In order to do this you can select the axis text and change x, y, dx, dy, text-anchor attributes accordingly, for example:
d3.select(".nv-x").selectAll(".tick text") .attr('y', 15);
In order to do this you can select the axis text and change x, y, dx, dy, text-anchor attributes accordingly, for example: