Venn Diagram entirely in CSS
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Join For FreeA friend of mine alerted me this weekend to just how much I have a weird fascination with Venn diagrams. I decided to roll with it. So yeah, I have an irrational love of Venn diagrams. But that begs the question, can I make a Venn diagram with just CSS?

I found a couple of examples out there:
But I felt like they had a bit too much fluff in the HTML markup. Not that there is anything technically wrong with their implementations. I prefer complexity in my CSS and not in my HTML. It's probably just a subjective thing, but I do.
So how do you do it?
First you create 3 divs. 1 for each Venn circle, and 1 for the overlap section. Each div contains a p with content in it.
<div id="venn"> <div><p>People Who like Venn Diagrams</p></div> <div><p>People who read my blog articles</p></div> <div id="overlap"><p>Just me.</p></div> </div>
Then you go to style each of the circles. Give them matching heights and widths, and a border radius of half of the height. This creates the circle. Then give each one an opacity below 1. This will ensure that when they overlap they will form a new color.
#venn div{ height: 360px; width: 360px; border-radius:180px; -khtml-border-radius:180px; -moz-border-radius:180px; -webkit-border-radius:180px; border: 1px solid #000; display: table; float: left; opacity: .6; }
I then created two rules based on the nth child css selector to color each of the circles. I also padded to ensure that there would be a space to write in the overlap section.
#venn div:nth-child(1){ background-color: #FF0000; color: #FFF; padding-right: 60px; } #venn div:nth-child(2){ background-color: #0000FF; color: #FFF; margin-left: -60px; padding-left: 60px; }
Finally I styled the overlap section using relative positioning and pulled it back towards the center.
#venn #overlap{ border: 0; height: 30px; width: 30px; left: -350px; top: 150px; color: #ccc; position: relative; text-align: center; z-index: 10; opacity: 1; }
The real trick is to watch the pixel counts because a couple are directly related.
To create a circle:
- width must equal height
- border radius must equal 50% of width.
To overlap circles:
- Circle 2 must have negative x left margin
- (Or Circle 1 must have negative x right margin)
- Each circle must have x padding-left or x padding-right to ensure its text doesn't spill over borders
It looks like the example works across modern browsers, including IE 9, but not previous versions.
Source: http://www.terrenceryan.com/blog/post.cfm/venn-diagram-entirely-in-css
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