You can use the linear-gradient property and manipulate the angle to create a split angle effect with a CSS linear gradient for the background colour. Here's an example of how you can achieve a split-angle effect:

body {
  margin: 0;
  height: 100vh;
  background: linear-gradient(135deg, #3498db 50%, #e74c3c 50%);
  background-size: cover;
  font-family: 'Arial', sans-serif;
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
}

h1 {
  font-size: 2em;
  margin: 0;
}

p {
  font-size: 1.2em;
  margin: 20px 0 0;
}

In this example:

• The linear-gradient property is used to create a gradient background.

• 135deg specifies the angle of the gradient, creating a split effect.

• #3498db and #e74c3c are the colours used for the gradient.

• 50% in the gradient indicates the point where the colours meet, creating the split effect.

You can change the colours, angles, and other styles as you like. This is just a simple example to help you begin.