For changing different aspects of your website, click 'design' in the upper navigation bar.
From there you can adjust the website in various ways:
1) Darker/lighter - this makes the website either more darker or lighter
<pic of dark/light>
2) Round/square - this makes the buttons of the website either round or square
<pic of round/square buttons>
3) Colourful/subtle - this makes the website's accent colour be either colourful or subtle