For a cleaner look, you may want to hide your chart's axis lines.
To do so, click the Settings tab in the top right corner of your chart's pop-up window.
Here you will see more controls for your chart. At Axis, slide the toggle off, making them invisible.
This should be how your chart looks like once you've turned the axis off - cleaner and uncluttered.
Please note that you might be accused of presenting misleading data if you do not provide reference points on your charts.