I want to achieve this using html and css:
I have tried to set the opacity of the container to 0.3 and the box to 1, but it doesn't work: both divs have 0.3 opacity.
The effect I am trying to achive is a popup box that comes on top of the page. It is highlighted by fading the content below (by lowering the opacity).
This might not be the most orthodox method but you can use a small semi-transparent background image for each div / container that repeats. It does seem that in this day and age you should be able to achieve this in pure (simple not hackish) css with no js but as the answers above show it isn't that straight forward...
Using a tiled image might seem dated but will work no worries across all browsers.
Apply this css rule
In addition to this, you have to declare background: transparent for IE web browsers.
For more details visit the following link:
http://robertnyman.com/2010/01/11/css-background-transparency-without-affecting-child-elements-through-rgba-and-filters/
Using
background-color: rgba(#777788, 0.3);
instead of opacity could maybe fix the problem.Hi you can used opicity with background color as like this
css
HTML
Live demo http://jsfiddle.net/rohitazad/yT6nG/29/
Another workaround is to simply use an overlay background to create a similar effect.
I personally like a black overlay with about a 65% opacity, but for what you are trying to do you may want to use a white overlay at round 70%.
Create a small (100 x 100 or less) PNG in Photoshop or GIMP that has the color and opacity you want. Then just set that as the background of your light box.
If you create multiple PNGs at different opacities you can easily switch between them with JS or dynamically at load via backend scripting.
It's not technically what you are trying to do, but aesthetically it can give a very similar effect and UX wise accomplishes the same thing. It is also very easy to do, and widely supported across pretty much everything.
As far as I know you can't do it in a simple way. There a couple of options here: 1. Use absolute positioning to position box "inside" the container.