Chart Axis Lines
For a cleaner look, you may want to hide your chart's axis lines.
To do so, click the Settings tab (the small gear icon) in the top right corner of your chart's pop-up window.
Here you will see more controls for your chart. For Axis, slide the toggle to the off position, thus making the lines invisible.
Please note that you might be accused of presenting misleading data if you do not provide reference points on your charts.