@lembi,
CanvasJS comes with in-build chart options to customize the chart elements. You can use the labelFontSize and labelFontColor properties to style the label font-size and font-color of both axes respectively as shown in the code snippet below –
axisX: {
labelFontSize: 20,
labelFontColor: "#628395"
},
axisY: {
labelFontSize: 20,
labelFontColor: "#628395"
},
Also, please take a look at this working JSFiddle for an example on customizing the axes label font-size and font-color.

___________
Indranil Deo
Team CanvasJS