You will notice that Spanish days are not capitalized; they are treated like ordinary words. They are capitalized when starting a sentence or standing alone, such as when used in a calendar. However, el often, but not always, precedes the day in question.
No me gustan los lunes. (I don’t like Mondays)
Sábado es el mejor día de la semana. (Saturday is the best day of the week.)
El domingo es para descansar. (Sunday is for rest.)
