There is a subtle difference between "little" and "a little", just as there is between "few" and "a few". Without the "a" there is a negative connotation. Eg "The coffee has a little sugar" can be interpreted literally, but "The coffee has little sugar" suggests it does not have enough sugar. Similarly "she has few friends" suggests she is not well liked, which is different from "she has a few friends".
(for those who are afraid to click on links):
Few - A few - Little - A little Danmoller
Here is how they relate to each other:<pre>
Few = poucos/poucas (plural because it's for countable quantities) A few = some = alguns, algumas Little = pouco/pouca (there is no plural because it's used for uncountable quantities) A little = um pouco de</pre>
Tenho poucos brinquedos = I have few toys. Tenho alguns brinquedos = I have a few toys = I have some toys. O copo tem pouca água = The glass has little water. O copo tem um pouco de água = The glass has a little water.</pre>
Go back to the Portuguese Help Index: https://www.duolingo.com/comment/6331998
No, it modifies "açucar", but as the people above mentioned, it has a negative meaning (not enough sugar), just like when we say in english, "the coffee has little sugar" or more naturally, "the coffee doesn't have very much sugar"/"the coffee has only a little sugar"... one of these phrases should be the translation given by duolingo, not "the coffee has a little sugar."