@bestdragon I don't know of any addons that specifically change a website to a lighter theme (light-to-dark addons are much more popular), but you may be able to use a custom stylesheet. Stylish is a popular extension for that:
And then, the readability of the editor IS MUCH IMPORTANT.
Yes, definitely. However, it's about what works best for the most people, and most developers prefer a dark theme. You're the first person I recall encountering who disliked the dark editor theme, and I've been helping out on the forums for a few years ¯\_(ツ)_/¯
Edit: If possible, tweaking your screen's color settings may help you see better on Codecademy too.
I don't mind using the dark theme, but when I am outside, it is very hard to use. I can barely find the cursor. Most other editors have a way to change the theme, so I can switch to light when outside.