Transparent arrow/triangle indented over an image

Question

I would like to make a transparent arrow over an image. This triangle should be indented in a semi transparent block and show the background image.

Answer 1

Simple Approach

• Use pseudo element with box-shadow and transform: rotate();

• Add overflow: hidden; to main div.

Snippet :

body {
  margin: 0;
  padding: 0;
  background: url(http://i.imgur.com/EinPKO3.jpg);
  background-size: cover;
}
div {
  height: 100px;
  width: 100%;
  position: absolute;
  bottom: 0;
  overflow: hidden;
}
div:before {
  position: absolute;
  top: -50px;
  left: calc(50% - 35px);
  content: "";
  height: 50px;
  width: 50px;
  background: transparent;
  -webkit-transform-origin: 0% 100%;
  -moz-transform-origin: 0% 100%;
  -ms-transform-origin: 0% 100%;
  transform-origin: 0% 100%;
  -webkit-transform: rotate(45deg);
  -moz-transform: rotate(45deg);
  -ms-transform: rotate(45deg);
  transform: rotate(45deg);
  box-shadow: 0 0 0 5000px rgba(0, 0, 0, 0.6);
}