<div class="container">
  <div class="triangle"></div>  
</div>

<div class="container">
  <div class="triangle-transparent"></div>
</div>
.triangle {
  border-left: 130px solid red;
  border-bottom: 130px solid #f9cb30;
}

.triangle-transparent {
  border-left: 130px solid transparent;
  border-bottom: 130px solid #f9cb30;
}

.container {
  width: 90%;
  margin: 30px auto;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.