Answer:
The powerful tone in “Invictus” is gloomy and dark although Henley remains optimistic and with the help of the three types of figurative language, the dark tone is constantly seen throughout the poem helping readers truly feel the misery the author is going through.
if you want the theme
The central theme of the poem "Invictus" is bravery. Henley references many dangerous or unfriendly elements in his story.