CSS Background Opacity [duplicate]

问题:

This question already has answers here:

How do I give text or an image a transparent background using CSS? (28 answers)

Closed 3 years ago.

I am using something similar to the following code:

<div style="opacity:0.4; background-image:url(...);">
    <div style="opacity:1.0;">
        Text
    </div>
</div>

I expected this to make the background have an opacity of 0.4 and the text to have 100% opacity. Instead they both have an opacity of 0.4.

回答1:

Children inherit opacity. It'd be weird and inconvenient if they didn't.

You can use a translucent PNG file for your background image, or use an RGBa (a for alpha) color for your background color.

Example, 50% faded black background:

<div style="background-color:rgba(0, 0, 0, 0.5);">
   <div>
      Text added.
   </div>
</div>

回答2:

You can use CSS 3 :before to have a semi-transparent background and you can do this with just one container. Use something like this

<article>
  Text.
</article>

Then apply some CSS

article {
  position: relative;
  z-index: 1;
}

article::before {
  content: "";
  position: absolute;
  top: 0; 
  left: 0;
  width: 100%; 
  height: 100%;  
  opacity: .4; 
  z-index: -1;
  background: url(path/to/your/image);
}

Sample: http://codepen.io/anon/pen/avdsi

Note: You might need to adjust the z-index values.

回答3:

The following methods can be used to solve your problem:

1. CSS alpha transparency method (doesn't work in Internet Explorer 8):

   #div{background-color:rgba(255,0,0,0.5);}
   

2. Use a transparent PNG image according to your choice as background.

3. Use the following CSS code snippet to create a cross-browser alpha-transparent background. Here is an example with #000000 @ 0.4% opacity

   .div {
       background:rgb(0,0,0);
       background: transparent\9;
       background:rgba(0,0,0,0.4);
       filter:progid:DXImageTransform.Microsoft.gradient(startColorstr=#66000000,endColorstr=#66000000);
       zoom: 1;
   }
   .div:nth-child(n) {
       filter: none;
   }
   

For more details regarding this technique, see this, which has an online CSS generator.

回答4:

I would do something like this

<div class="container">
  <div class="text">
    <p>text yay!</p>
  </div>
</div>

CSS:

.container {
    position: relative;
}

.container::before {
    position: absolute;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
    background: url('/path/to/image.png');
    opacity: .4;
    content: "";
    z-index: -1;
}

It should work. This is assuming you are required to have a semi-transparent image BTW, and not a color (which you should just use rgba for). Also assumed is that you can't just alter the opacity of the image beforehand in Photoshop.

回答5:

You can use Sass' transparentize.

I found it to be the most useful and plain to use.

transparentize(rgba(0, 0, 0, 0.5), 0.1) => rgba(0, 0, 0, 0.4)
transparentize(rgba(0, 0, 0, 0.8), 0.2) => rgba(0, 0, 0, 0.6) 

See more: #transparentize($color, $amount) ⇒ Sass::Script::Value::Color

回答6:

.transbg{/* Fallback for web browsers that don't support RGBa */
background-color: rgb(0, 0, 0);
/* RGBa with 0.6 opacity */
background-color: rgba(0, 0, 0, 0.6);
/* For IE 5.5 - 7*/
filter:progid:DXImageTransform.Microsoft.gradient(startColorstr=#99000000, endColorstr=#99000000);
/* For IE 8*/
-ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorstr=#99000000, endColorstr=#99000000)";}

回答7:

This is because the inner div has 100% of the opacity of the div it is nested in (which has 40% opacity).

In order to circumvent it, there are a few things you could do.

You could create two separate divs like so:

<div id="background"></div>
<div id="bContent"></div>

Set your desired CSS opacity and other properties for the background and use the z-index property (z-index) to style and position the bContent div. With this you can place the div overtope of the background div without having it's opacity mucked with.

---

Another option is to RGBa. This will allow you to nest your divs and still achieve div specific opacity.

---

The last option is to simply make a semi transparent .png image of the color you want in your desired image editor of choice, set the background-image property to the URL of the image and then you won't have to worry about mucking about with the CSS and losing the capability and organization of a nested div structure.

回答8:

Just make sure to put width and height for the foreground the same with the background, or try to have top, bottom, left and right properties.

<style>
    .foreground, .background {
        position: absolute;
    }
    .foreground {
        z-index: 1;
    }
    .background {
        background-image: url(your/image/here.jpg);
        opacity: 0.4;
    }
</style>

<div class="foreground"></div>
<div class="background"></div>