Which one is better - opacity, rgba(), or something else? To blur the background-element

Maybe you had a lot of hard times like I had, trying to blur the background element without affecting its inner contents such as child elements, text, borders, etc.

In my case, as the first thought, I turned to the opacity to do the job.

And the next moment, I got a weird result and thought about another option.

Which was rgba() and, it worked for me.

But, it's not the problem. If the alpha value of rgba() can do the job, why do we need the opacity in any way?

It seems there are some questions to be solved, right?

So let's dig into the details.

We have a blue color inner element and orange color background element like below.

And, we want the background element to be blurred, like below.

To get that output, we can try the following options.

Using two separate elements
Using opacity for the parent element
Using rgba() for the parent element
Changing visibility to hidden or color to transparent (to completely hide the background element)

Let's try these options one by one to achieve our requirements.

1. Using two separate elements

Here, we have two separate div called outside-div and inside-div


<body>

 <div id="outside-div"></div>
 <div id="inside-div"></div>

</body>

In the CSS, before doing anything, let's center everything on the screen in the first place.

Here, we use flexbox to do the job.


body {
 display: flex;
 justify-content: center;
 align-items: center;
}

Then, give some width, height and background-color to the outside-div and inside-div.


#outside-div {
 width: 400px;
 height: 400px;
 background: rgb(255, 165, 0);
}


#inside-div {
 width: 200px;
 height: 200px;
 background: rgb(0, 0, 255);
}

And, to drag both div a bit down from the top of the screen, we can use position: absolute and top: 25% for both elements.


#outside-div {
 position: absolute;
 top: 25%;
}


#inside-div {
 position: absolute;
 top: 25%;
}

Next, we have to center the inside-div inside the outside-div.

To do that, we can set the margin-top value like below.

margin-top for the innermost div = ((height of outermost div) - (height of innermost div))/ 2


#inside-div {
 margin-top: 100px;
}

Now, set the opacity as 0.3 of the outside-div.


#outside-div { 
 opacity: 0.3; 
}

And, here is our complete CSS code.


* {
 box-sizing: border-box;
 margin: 0;
 padding: 0;
}

body {
 display: flex;
 justify-content: center;
 align-items: center;
}

#outside-div {
 position: absolute;
 top: 25%;
 width: 400px;
 height: 400px;
 background: rgb(255, 165, 0);
 opacity: 0.3; 
}


#inside-div {
 position: absolute;
 width: 200px;
 height: 200px;
 top: 25%;
 margin-top: 100px;
 background: rgb(0, 0, 255);
}

Oh, it works!

Finally, we're finished with solving the problem!

But hold on, why are we only using two separate elements?

Is there any luck with parent and child elements, or maybe, an element with its pseudo (:before or :after) element instead, where we should have to use them?

Well, the answer is YES!

However, some of them can be a bit tricky.

So let's take a look at how to blur a background element that has a child element/pseudo-element as its inner element.

2. Using opacity for the parent element

One of the ways to blur an element is using the opacity property.

In simple words, the opacity sets the see-through (transparent) level of an element. If its value is,

1 :- which means there's no transparency at all (default value).
0 :- which means it is fully transparent.
0.5 :- which means see-through level is 50%.

So let's try to use opacity.

Here is our HTML code.


<body>

<div id="box"></div>

</body>

Using opacity - 1st Attempt:

So, we have a div element called #box and its pseudo-element (#box:before) in it.


#box { 
 width: 400px;
 height: 400px;
 background: rgb(255, 165, 0);
}

#box:before {
 content: "";
 width: 200px;
 height: 200px;
 background: rgb(0, 0, 255);
}

As the first thing, let us place them neatly.

Also, make the position as absolute of the #box and push it down by 25% away from the screen.


body {
 display: flex;
 justify-content: center;
 align-items: center;
}

#box {
 position: absolute;
 top: 25%;
 display: flex;
 justify-content: center;
 align-items: center; 
}

#box:before {
 content: "";
 position: absolute;
}

As the final thing, set the opacity of the #box as 0.3.


#box {
 opacity: 0.3; 
}

Here is the complete CSS code.


body {
 display: flex;
 justify-content: center;
 align-items: center;
}

#box {
 position: absolute;
 top: 25%;
 width: 400px;
 height: 400px;
 display: flex;
 justify-content: center;
 align-items: center; 
 background: rgb(255, 165, 0);
 opacity: 0.3; 
}

#box:before {
 content: "";
 position: absolute;
 width: 200px;
 height: 200px;
 background: rgb(0, 0, 255);
}

Here is the visual result that we've got.

Okay, I know what you are thinking right now. Because it isn't the result that we expected, right?

We only want to make the opacity of the #box as 0.3 and opacity of the #box:before as 1 (default opacity).

Using opacity - 2nd Attempt:

To fix the problem, let's follow these steps.

Step 1: Swap width and height values between #box and #box:before


 /* step 1 */

#box {
 width: 200px;
 height: 200px;
}

#box:before {
 content: "";
 width: 400px;
 height: 400px;
}

Step 2: Change the top property from top: 25% to top: calc(25% + 100px) of the #box

By doing so, #box:before can be placed exactly 25% down from the screen top.


/* step 2 */

#box {
 position: absolute;
 top: calc(25% + 100px);
}

Step 3: Set z-index

for the #box: z-index: 2
for the #box:before: z-indx: 1

By doing so, #box:before will be pushed behind the #box.


/* step 3 */

#box {
 z-index: 2; 
}

#box:before {
 z-index: 1;
}

Step 4: Set opacity: 0.3 to the #box:before


/* step 4 */

#box:before {
 opacity: 0.3;
}

Complete CSS code is like below.


#box {
 position: absolute;
 top: calc(25% + 100px);
 width: 200px;
 height: 200px;

 display: flex;
 justify-content: center;
 align-items: center;

 background: rgb(0, 0, 255);

 z-index: 2; 
}

#box:before {
 content: "";
 position: absolute;

 width: 400px;
 height: 400px;

 background: rgb(255, 165, 0);

 opacity: 0.3; 

 z-index: 1;
}

Now you'll get the following result as you expected.

3. Using rgba() for the parent element

Let's try another way to get the expected result. And, it is the most simple one.

All you need to do is, remove the opacity: 0.3 from #box and change its background-color as rgba() colors and set your opacity as the fourth value there.


#box {
 position: absolute;
 top: 25%;
 width: 400px;
 height: 400px;
 display: flex;
 justify-content: center;
 align-items: center; 

 /* change rgba() color like this */

 background: rgba(255, 165, 0, 0.3);
}

#box:before {
 content: "";
 position: absolute;
 width: 200px;
 height: 200px;
 background: rgb(0, 0, 255);
}

This is the final result.

4. Changing visibility to hidden or color to transparent (to completely hide the background element)

If your requirement is only to make the background div as invisible, it's better to make the child element/pseudo-element as visible and the background (parent) element as invisible.

You can use this code for it.


#box {
 visibility: hidden;
 position: absolute;
 top: 25%;
 width: 400px;
 height: 400px;
 display: flex;
 justify-content: center;
 align-items: center; 
 background: rgb(255, 165, 0);
}

#box:before {
 visibility: visible;
 content: "";
 position: absolute;
 width: 200px;
 height: 200px;
 background: rgb(0, 0, 255);
}

Or you can use color: transparent for the background (parent) element.


#box {
 background: transparent;
}

#box:before {
 background: rgb(0, 0, 255);
}

Which one is better - opacity or rgba()?

Now, let us turn into the ideal question which one is better?

By looking at methods that used opacity and rgba() that we discussed above, you might be wondering which one is better to use for your specific case.

Well, as always, it depends.

However, let me explain some of the differences between both of them.

The value of opacity applies to the whole element, including its child elements, text, borders, colors, etc.
In the meantime, the alpha value of the rgba() only applies to the color of that particular element.

So that's the reason you got the #box:before as blurred at our 1st attempt where we used opacity to blur only the background element.

Also, for the same reason, you may feel some visual differences between the two results where we got the expected result using opacity and rgba().

In my opinion, it is better to use rgba() if you only want to blur the background element.

Conclusion

As the last thing, let me recap what you exactly got from this article.

a few ways to blur the background element without affecting its inner contents.
some sense of the difference between opacity and rgba()
some sense of where to use opacity and where to use rgba() based on your specific requirement.

I hope you enjoyed this article, and you can support me at ko-fi. I always appreciate your support. It really encourages me to keep going.

Happy Coding!