CSS Shapes - Triangles

CSS Shapes - Triangles

Chris Bongers
·Mar 24, 2021·

4 min read

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Yesterday we had our first introduction in CSS Shapes and started with the basic shapes.

Today I want to check out a very useful and a bit of an odd shape. The triangle has many ways of building, but most people use the border hack to create them.

Creating triangles in CSS

Let's create a basic down carrot.

<div class="triangle-down"></div>

For the demo purpose, I added some colors to see what actually makes it appear like a triangle.

.triangle-down {
  width: 0;
  height: 0;
  border-left: 50px solid red;
  border-right: 50px solid purple;
  border-top: 100px solid blue;
}

The actual magic part is the border-top. We'll see that's what we'll see, but we are offsetting the left and right by half of it. In the example, I added a red and purple color.

This will result in the following:

CSS Triangle

As you can see, the result is looking like a triangle. To make this perfect, we need to set the sides to transparent.

.triangle-down {
  width: 0;
  height: 0;
  border-left: 50px solid transparent;
  border-right: 50px solid transparent;
  border-top: 100px solid blue;
}

CSS Down triangle

Let's say we want the arrow to point up and not down. We can simply switch the border-top to be border-bottom.

.triangle-up {
  width: 0;
  height: 0;
  border-left: 50px solid transparent;
  border-right: 50px solid transparent;
  border-bottom: 100px solid blue;
}

CSS Arrow up

The same can be applied to make left and right arrows:

.triangle-left {
  width: 0;
  height: 0;
  border-top: 50px solid transparent;
  border-left: 100px solid blue;
  border-bottom: 50px solid transparent;
}
.triangle-right {
  width: 0;
  height: 0;
  border-top: 50px solid transparent;
  border-right: 100px solid blue;
  border-bottom: 50px solid transparent;
}

This is basically the same concept, but we switch around by defining the top and bottom and using the left and right as offsets with a color.

Left and right arrow in CSS

You can even offset triangles to point to a specific corner. For instance point to left bottom:

.triangle-left-bottom {
  width: 0;
  height: 0;
  border-bottom: 100px solid blue;
  border-right: 100px solid transparent;
}

Left bottom triangle in CSS

Can you figure out how to create the other corners?

You can always have a play with this Codepen.

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