style.css

:root {
  --width: 300px;
  --height: 100px;
  --top-color: #f44336;
  --bottom-color: #2196F3;
}

.separator {
  position: relative;
  width: var(--width);
  height: var(--height);
}

.separator::before {
  position: absolute;
  content: "";
  width: 100%;
  height: 100%;
  background-color: var(--top-color);
  clip-path: polygon(100% 0, 0 0, 0 100%);
}

.separator::after {
  position: absolute;
  content: "";
  width: 100%;
  height: 100%;
  background-color: var(--bottom-color);
  clip-path: polygon(100% 0, 0 100%, 100% 100%);
}

.separator.reverse {
  transform: rotateY(180deg);
}

.vertical .separator.reverse {
  transform: rotateX(180deg);
}