CSS can be used to create various shapes like circles, triangles, and squares. While this technique is slowly falling out of favor, it can sometimes be worth using for simple shapes, instead of using SVG or images.

https://codepen.io/chalarangelo/pen/gOJOwwo

Square & Rectangle

A simple CSS square can be created by setting the width and height to the same value. Similarly, a rectangle can be created by setting the width and height to different values.

<div class="square"></div>
<div class="rectangle"></div>

.square {
  width: 64px;
  height: 64px;
  background: #5394fd;
}

.rectangle {
  width: 128px;
  height: 64px;
  background: #5394fd;
}

Circle & Ellipse

Using the border-radius property, a circle can be created by setting it to 50%. The width and height must be the same to create a circle. Subsequently, an ellipse can be created by providing two values for the border-radius and setting the width and height to different values.

<div class="circle"></div>
<div class="ellipse"></div>

.circle {
  width: 64px;
  height: 64px;
  border-radius: 50%;
  background: #5394fd;
}

.ellipse {
  width: 128px;
  height: 64px;
  border-radius: 64px / 32px;
  background: #5394fd;
}

Triangles

A triangle can be created by using three borders. The border-width should be the same for all borders, and the opposite side of where the triangle points towards should have the desired border-color. The adjacent borders should have a border-color of transparent.

<div class="triangle-down"></div>
<div class="triangle-up"></div>
<div class="triangle-left"></div>
<div class="triangle-right"></div>

.triangle-down {
  width: 0;
  height: 0;
  border-top: 32px solid #5394fd;
  border-left: 32px solid transparent;
  border-right: 32px solid transparent;
}

.triangle-up {
  width: 0;
  height: 0;
  border-bottom: 32px solid #5394fd;
  border-left: 32px solid transparent;
  border-right: 32px solid transparent;
}

.triangle-left {
  width: 0;
  height: 0;
  border-right: 32px solid #5394fd;
  border-top: 32px solid transparent;
  border-bottom: 32px solid transparent;
}

.triangle-right {
  width: 0;
  height: 0;
  border-left: 32px solid #5394fd;
  border-top: 32px solid transparent;
  border-bottom: 32px solid transparent;
}