How to get 'div' shaped as a flag with CSS

Question

I want to add a label on some of my elements on a website and design for a label that is a flag with an inverted V-shaped cut at the bottom.

So far I have this:

Answer 1

With CSS:

You can use CSS transforms on pseudo elements to create the background with a transparent inverted triangle at the bottom:

body{background:url('http://lorempixel.com/image_output/food-q-c-640-480-1.jpg');background-size:cover;}
p{
  position: relative;
  width: 150px; height: 150px;
  overflow: hidden;
  border-top:3px solid #EF0EFE;
}
p:before, p:after{
  content: '';
  position: absolute;
  top: -3px;
  height: 100%; width: 50%;
  z-index: -1;
  border:2px solid #EF0EFE;
  box-sizing:border-box;
}
p:before{
  left: 0;  
  transform-origin: 0 0;
  transform: skewY(-20deg);
  border-width:0 0 4px 3px;
}
p:after{
  right: 0;
  transform-origin: 100% 0;
  transform: skewY(20deg);
  border-width:0 3px 4px 0;
}

Some text ... 

Note that you will need to add vendor prefixes on the transform and transform-origin properties to maximize browser support. See canIuse for more information.

---

With SVG

Another approach is to use an inline SVG with the polygon element:

body{background: url('http://lorempixel.com/image_output/food-q-c-640-480-1.jpg');background-size: cover;}
div{position: relative;width: 100px; height: 150px;}
svg{position: absolute;width: 100%;height: 100%;z-index: -1;}

  
  
Some text ...