I have a project where I need to insert speech bubbles / message boxes. The general shape I am trying to achieve is this one :

.bubble {
  height: 100px;
  width: 200px;
  border: 3px solid gray;
  background: lightgray;
  position: relative;
  cursor:pointer;
}
.triangle {
  width: 0;
  border-top: 20px solid black;
  border-left: 20px solid transparent;
  border-right: 20px solid transparent;
  cursor:pointer;
}

<div class="bubble">Speech bubble
</div>
<div class="triangle">
</div>

This currently does not pass a hit-test as the transparent border is also clickable.

Objectives

• The hit box (clickable / hoverable areas) needs to stick to the shape's boundaries (the transparent borders here are also hoverable, invalidating this).

• I need to display the shape over various content (images, gradents, text...),

Issues

The main issues I am having when manipulating this shape are:

• Have the ability to move the triangle around the speech bubble according to the position of the element it refers to (top/left/right/bottom sides)
• adding a border or box shadow around it when emphasis is needed

Is there anyway of addressing these issues?

解决方案

In order to achieve this, you should consider altering your markup in order to make your html more efficient. This can be achieved using a pseudo element. I'll address each point individually, and put it all together at the end of my answer.

First of all,

Use pseudo elements to avoid extra elements

You could use a pseudo element to remove the extra .triangle div. This not only reduces your div numbers, but also helps with positioning as you can use the top: left: right: and bottom: css properties in order to position according to your main element. This can be seen below:

.oneAndOnlyDiv {
  height: 100px;
  width: 200px;
  border: 3px solid gray;
  background: lightgray;
  position: relative;
}
.oneAndOnlyDiv:before {
  content: "";
  position: absolute;
  top: 100%;
  left: 20px;
  width: 0;
  border-top: 20px solid black;
  border-left: 20px solid transparent;
  border-right: 20px solid transparent;
}

<div class="oneAndOnlyDiv">Main div</div>

---

Hit testing

In order to create your "hit test", you may wish to use a rotated element instead of a border hack.

Something like:

div {
  height: 100px;
  width: 200px;
  background: gray;
  position: relative;
  cursor:pointer;
}
div:before {
  content: "";
  position: absolute;
  top: 100%;
  left: 20px;
  height: 20px;
  width: 20px;
  background: black;
  transform: rotate(45deg);
  transform-origin:top right;
}

<div>Only element</div>

or use a skewed pseudo element:

div {
  height: 100px;
  width: 200px;
  background: gray;
  position: relative;
  cursor:pointer;
}
div:before {
  content: "";
  position: absolute;
  top: 90%;
  left: 20px;
  height: 30%;
  width: 20px;
  background: black;
  transform: skewY(-45deg);
  transform-origin:bottom left;
  z-index:-1;
}

<div>Only element</div>

which will show the pointer only when the square or main element is hovered. But hang on, that messes up the positioning? how can you deal with that?

There are a few solutions to that. One of which is to use the calc CSS property.

div {
  height: 100px;
  width: 200px;
  background: gray;
  position: relative;
  cursor:pointer;
}
div:before {
  content: "";
  position: absolute;
  top: -webkit-calc(100% - 10px); /*may require prefix for old browser support*/
  top: calc(100% - 10px); /*i.e. half the height*/
  left: 20px;
  height: 20px;
  width: 20px;
  background: gray;
  transform: rotate(45deg);
}

<div>Only element</div>

Adding a border

You can add a border quite easily now, simply by adding a border declaration to the main element, and setting the border-bottom and border-right of the pseudo element to inherit

Border

div {
  height: 100px;
  width: 200px;
  background: gray;
  position: relative;
  cursor:pointer;
  border:3px double black;
}
div:before {
  content: "";
  position: absolute;
  top: -webkit-calc(100% - 10px); /*may require prefix for old browser support*/
  top: calc(100% - 10px); /*i.e. half the height*/
  left: 20px;
  height: 20px;
  width: 20px;
  background: gray;
  transform: rotate(45deg);
  border-bottom:inherit;
  border-right:inherit;
  box-shadow:inherit;
}

<div>Only element</div>

Box Shadow:

In order to have a box shadow, I've used the :after pseudo element in order to hide the box shadow over the other pseudo, making the element seem as one single element.

div {
  height: 100px;
  width: 200px;
  background: gray;
  position: relative;
  cursor:pointer;
  box-shadow: 5px 5px 10px 2px black;
}
div:before,div:after {
  content: "";
  position: absolute;
  top: -webkit-calc(100% - 10px); /*may require prefix for old browser support*/
  top: calc(100% - 10px); /*i.e. half the height*/
  left: 20px;
  height: 20px;
  width: 20px;
  background: gray;
  transform: rotate(45deg);
z-index:-1;
  box-shadow:inherit;
}
div:after{
  box-shadow:none;
  z-index:8;
  }

<div>Only element</div>

Putting it all together

You can also add a border radius to your message box or speech bubble by again, using the border-radius property:

div {
  height: 100px;
  width: 200px;
  background: gray;
  position: relative;
  cursor:pointer;
  border:3px double black;
  border-radius:10px;
}
div:before {
  content: "";
  position: absolute;
  top: -webkit-calc(100% - 10px); /*may require prefix for old browser support*/
  top: calc(100% - 10px); /*i.e. half the height*/
  left: 20px;
  height: 20px;
  width: 20px;
  background: gray;
  transform: rotate(45deg);
  border-bottom:inherit;
  border-right:inherit;
  box-shadow:inherit;
}

<div>Only element</div>

This even allows you to create not only a triangle, but how about a circle instead?

div {
  height: 100px;
  width: 200px;
  background: gray;
  position: relative;
  cursor:pointer;
  border:3px double black;
  border-radius:10px;
}
div:before {
  content: "";
  position: absolute;
  top: -webkit-calc(100% - 13px); /*may require prefix for old browser support*/
  top: calc(100% - 13px); /*i.e. half the height + border*/
  left: 20px;
  height: 20px;
  width: 20px;
  background: gray;
  transform: rotate(45deg);
  border:3px double transparent;
  border-bottom:inherit;
  border-right:inherit;
  box-shadow:inherit;
  border-radius:50%;
}

<div>Only element</div>

If you are having issues with content overflowing and being 'hidden' behind this pseudo element, and you aren't fussed about having a border, you could use a negative z-index which will solve this issue.

Don't like using 'magic numbers'?

If you don't like the idea of using a calc value, in which the positioning in my answer is currently using (whilst working), you may wish to use transform:translate(50%)

This would be a much better approach, since:

• You do not need to know the size of the border, nor half the width
• You will be making your message box/ bubble a lot more dynamic in its positioning, and would support further sizings.

div {
  height: 100px;
  width: 200px;
  background: gray;
  position: relative;
  cursor: pointer;
  border: 3px double black;
  border-radius: 10px;
}
div:before {
  content: "";
  position: absolute;
  top: 100%;
  left: 30px;
  height: 20px;
  width: 20px;
  background: gray;
  box-sizing:border-box;
  transform: rotate(45deg) translate(-50%);
  border-bottom: inherit;
  border-right: inherit;
  box-shadow: inherit;
}

<div>Only element</div>

Want to move it? You can!

div {
  height: 100px;
  width: 200px;
  background: gray;
  position: relative;
  cursor: pointer;
  border: 3px double black;
  border-radius: 10px;
}
div:before {
  content: "";
  position: absolute;
  top: 100%;
  left: 10%;
  height: 20px;
  width: 20px;
  background: gray;
  box-sizing: border-box;
  transform: rotate(45deg) translate(-50%);
  border-bottom: inherit;
  border-right: inherit;
  box-shadow: inherit;
  transition: all 0.8s;
}
div:hover:before {
  left: 90%;
}

<div>Only element</div>

Want it one the right?

div {
  height: 100px;
  width: 200px;
  background: gray;
  position: relative;
  cursor: pointer;
  border: 3px double black;
  border-radius: 10px;
}
div:before {
  content: "";
  position: absolute;
  top: 15%;
  left: 100%;
  height: 20px;
  width: 20px;
  background: gray;
  box-sizing:border-box;
  transform: rotate(45deg) translate(-50%);
  border-top: inherit;
  border-right: inherit;
  box-shadow: inherit;
  transition:all 0.8s;
}
div:hover:before{
  top:80%;
  }

<div>Only Element</div>

Want it to be a different shape of triangle?

div {
  height: 100px;
  width: 200px;
  background: gray;
  position: relative;
  cursor: pointer;
  border-radius: 10px;
}
div:before {
  content: "";
  position: absolute;
  top: 70%;
  left: 100%;
  height: 20px;
  width: 20px;
  background: gray;
  box-sizing:border-box;
  transform:  translate(-50%) skewX(45deg);
  box-shadow: inherit;
  transition:all 0.8s;
  z-index:-1;
}
div:hover:before{
  transform:  translate(-50%);
  border-radius:50%;
  top:20%;
  }

<div>Only Element</div>