You misplaced the closing "
twice:
if(yourChoice === "paper")
document.write("<h1 style='text-align:center;font-size:50;'>Muahaha! I have cut you down with the villanny of scissors!</h1>")
if(yourChoice === "scissors")
document.write("<h1 style='text-align:center;font-size:50;'>Go and weep! For I have crushed your devilish scissors with the might of my rock!</h1>")