Speech bubbles with CSS

Speech bubbles have existed in comics for decades, and they are a great way to visually represent dialogue. You can create a similar effect using CSS, by adding a triangle to the top of a content container.
For this task, you'll leverage the ::before and ::after pseudo-elements to create two triangles. The colors of the two triangles should be the same as the container's border-color and the container's background-color respectively.
The border-width of the one triangle (::before) should be 1px wider than the other one (::after), in order to act as the border. The smaller triangle (::after) should be 1px to the right of the larger triangle (::before) to allow for its left border to be shown.
And with that, you have a content container with a triangle at the top, much like a speech bubble. You can tweak this effect to also place the triangle at the bottom, left, or right of the container, or even create a different shape altogether.
https://codepen.io/chalarangelo/pen/dyxYOap

.container {
  position: relative;
  background: #ffffff;
  border: 1px solid #dddddd;
}

.container::before,
.container::after {
  content: '';
  position: absolute;
  bottom: 100%;
  left: 19px;
  border: 11px solid transparent;
  border-bottom-color: #dddddd;
}

.container::after {
  left: 20px;
  border: 10px solid transparent;
  border-bottom-color: #ffffff;
}

The border-width of the one triangle (::before) should be 1px wider than the other one (::after), in order to act as the border. The smaller triangle (::after) should be 1px to the right of the larger triangle (::before) to allow for its left border to be shown.
And with that, you have a content container with a triangle at the top, much like a speech bubble. You can tweak this effect to also place the triangle at the bottom, left, or right of the container, or even create a different shape altogether.
https://codepen.io/chalarangelo/pen/dyxYOap

From 30-seconds-of-code: speech-bubble