Use css to create a custom arrow shape [duplicate]

Answer 1

demo

#flag:before,
#flag:after{ 
  content: ""; 
  position: absolute; 
  border: 40px solid #231f20;
}
#flag:before { 
  left: -35px;
  border-left: 35px solid transparent;
}
#flag:after {
  right:-80px;
  border: 40px solid transparent;
  border-left: 40px solid #231f20;
}