One possible theme could be hope. The spark represents a glimmer of hope in the darkness.
Resilience is another theme. Just as a spark can start a fire and endure against the surrounding darkness, the characters in the story might show great resilience. They keep going despite the difficulties, and the spark is what drives them forward.
Isolation could be a theme. In the dark, one can feel very alone. If it's a story about a person in a dark place, they might be cut off from others and have to deal with their situation by themselves. Also, survival can be a theme. If the 'in the dark' situation is dangerous, like in a dark cave full of hazards, the characters would be focused on surviving.
Isolation could be a theme. A dark tale might be set in a desolate place or the characters might be isolated in some way, which adds to the overall sense of gloom. Also, the theme of loss can be present. This could be the loss of a loved one, of innocence, or of hope, all of which contribute to the darkness of the story. For example, in a story where a character has lost their family in a tragic event, it sets a very dark mood.
One possible theme could be fear. The darkness of the room can symbolize the unknown, which often induces fear in people.
Another theme might be isolation. At night, especially if it's very dark, a person can feel alone and cut off from the rest of the world. This sense of isolation can be a strong theme in the story.
One possible theme could be fear. The very idea of a dark house often evokes a sense of unease and terror. Another theme might be mystery. There could be secrets hidden within the walls of the house that the characters are trying to uncover. For example, the mystery of what happened to the previous owners or what lurks in the attic.
Fear is a likely theme. The darkness of the room can symbolize the unknown which often induces fear in people.
One possible theme is fear. The face in the dark is likely to evoke fear in the characters and the readers. Another theme could be the unknown. Since the face is in the dark, it represents something that is not fully known or understood.
One possible theme could be mystery. If the roommate is acting strange or has secrets, mystery would be a big part of it.
One possible theme could be isolation. Kirby might be alone in a world filled with darkness, which emphasizes his struggle. Another theme could be redemption. If there are characters that have been corrupted, Kirby could try to redeem them.
One possible theme could be mystery. Since it's a 'dark gumball story', there are likely elements that are not immediately clear, like the origin or purpose of the gumball.