You can add HTML, CSS and JavaScript to your pages.
To do that, click on the blue (+) 
you see when hovering between the different sections.
You’ll see a menu on the left with different types of stripes to choose from.
At the bottom of this menu, click Elements and choose RAW or HTML from the options on the right:
The RAW element adds your code to that of the entire site, while the HTML element adds it to the specfic page.
You now have a new stripe entirely dedicated to your code.
Click on the element stripe and select Edit Raw 
When you’re done editing the code, click SAVE.
If the element you chose to add was HTML:
Click on it and select Edit HTML 
Enter the code, then click SAVE