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In the sunset glow, the western sky burns bright red.
Literal
Sunset-glow [because-で] western sky [topic-は] bright-red-[adverbially-に] shine.
A painterly descriptive sentence. 夕焼け is the sunset's colored glow (the noun for the visual phenomenon, from 夕 'evening' + 焼け 'burning'). 真っ赤 ('bright red, deep red') uses the intensifying prefix 真っ- ('truly, perfectly,' used with colors and a few other words). 輝く ('to shine, glitter, radiate') conveys brilliance rather than mere light. Reads like a haiku observation.