CSS with Triangles on left Side

Question

Following Situation:

I try to make a Triangle, stick to the left side of my Website

.right_5 {
  margin-top: 0px;
  border-top: 350px solid transparent;
  border-bottom: 380px solid transparent;
  border-left: 350px solid black;
  z-index: 2;
}

<div class="right_5"></div>

And this is the Code, BUT

How do I Make it 100% of the left side? so that the top of the triangle points to the middle of the website?