Again, without knowing the exact story, possible themes could be despair. If it's a story about a difficult time, despair would likely be a big part of it.
One possible theme could be hope. If it's based on a true story, even during the darkest times, there must be some glimmer of hope that the characters hold on to, just like in real - life difficult situations.
The meaning of Endless Night was that the night was endless, representing the depth and length of the night. This term had a deep heritage in culture, and it had been passed down from the Book of Songs to this day. People liked to use Endless Night to express their anticipation for the unknown return and future, as well as their longing and anticipation for those who had left. Endless Night was also used to describe the difficult journey of waiting and anticipation, revealing strong emotions and the desire for reunion. In ancient poetry, the meaning of 'Endless Night' had many variations, such as describing the distance of space or the boundless meaning. In general, Endless Night symbolized the hope for the unknown and the future. It had a positive meaning.
Well, 'Endless Summer' is typically not based on real events. It might draw inspiration from various sources but is mainly a fictional creation to offer an enjoyable reading experience.