聚萤映雪

jù yíng yìng xuě

lit. to collect fireflies and study by their light (idiom); fig. ambitious student from impoverished background

burning the midnight oil

聚

jù

to assemble; to gather (transitive or intransitive)

萤

yíng

firefly

映

yìng

old variant of 映[ying4]

雪

xuě

snow