"Everyday" is an adjective; "every day" is an adverb. An adverb is needed for the sentence "Yo estudio español todos los días" because every day modifies the verb study.
If you're using Android, you can set up a bilingual keyboard in the keyboard settings.
If you're using Windows 10, you can add a keyboard language "English - international" and it will let you type accents by pressing apostrophe before the letter.
If you're using Mac, hold down the letter key and type the number of the accented letter.
I can't help you if you're using iPhone or Windows < 10
duolingo is looking to help people learn the exact translations and differences between the translations. "i study spanish daily" is "yo estudio español diariamente" which although means basically the same thing, it´s different than saying "i study spanish every day" . you´re not wrong, you´re simply not the most correct that you could be. :)