Default screen turn off no matter what! [Solved]

I'm new at this so don't get mad at me:
lately i installed resurrection remix rom (4.4.2), and whenever I'm watching a video on YouTube or playing 8ball(or any other game) , the screen turns of after 30 seconds if i don't touch it. it's so frustrating since I'm used to watch movies at work
what can i do?
thanks in advance

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