[css] How do I make a semi transparent background?

I need to make a white background 50% transparent without affecting anything else. How do I do it?

Good to know

Some web browsers have difficulty to render text with shadows on top of transparent background. Then you can use a semi transparent 1x1 PNG image as a background.

Note

Remember that IE6 don’t support PNG files.

Although dated, not one answer on this thread can be used universally. Using rgba to create transparent color masks - that doesn't exactly explain how to do so with background images.

My solution works for background images or color backgrounds.

#parent {_x000D_
    font-family: 'Open Sans Condensed', sans-serif;_x000D_
    font-size: 19px;_x000D_
    text-transform: uppercase;_x000D_
    border-radius: 50%;_x000D_
    margin: 20px auto;_x000D_
    width: 125px;_x000D_
    height: 125px;_x000D_
    background-color: #476172;_x000D_
    background-image: url('https://unsplash.it/200/300/?random');_x000D_
    line-height: 29px;_x000D_
    text-align:center;_x000D_
}_x000D_
_x000D_
#content {_x000D_
    color: white;_x000D_
    height: 125px !important;_x000D_
    width: 125px !important;_x000D_
    display: table-cell;_x000D_
    border-radius: 50%;_x000D_
    vertical-align: middle;_x000D_
    background: rgba(0,0,0, .3);_x000D_
}

<h1 id="parent"><a href="" id="content" title="content" rel="home">Example</a></h1>

This works, but all the children of the element with this class will also become transparent, without any way of preventing that.

.css-class-name {
    opacity:0.8;
}

Try this:

.transparent
{ 
  opacity:.50;
  -moz-opacity:.50; 
  filter:alpha(opacity=50); 
}

This is simple and sort. Use hsla css function like below

.transparent {
   background-color: hsla(0,0%,4%,.4);
}

If you want to make transparent background is gray, pls try:

   .transparent{
       background:rgba(1,1,1,0.5);
   }

div.main{
     width:100%;
     height:550px;
     background: url('https://images.unsplash.com/photo-1503135935062-
     b7d1f5a0690f?ixlib=rb-enter code here0.3.5&ixid=eyJhcHBfaWQiOjEyMDd9&s=cf4d0c234ecaecd14f51a2343cc89b6c&dpr=1&auto=format&fit=crop&w=376&h=564&q=60&cs=tinysrgb') no-repeat;
     background-position:center;
     background-size:cover 
}
 div.main>div{
     width:100px;
     height:320px;
     background:transparent;
     background-attachment:fixed;
     border-top:25px solid orange;
     border-left:120px solid orange;
     border-bottom:25px solid orange;
     border-right:10px solid orange;
     margin-left:150px 
}

DO NOT use a 1x1 semi transparent PNG. Size the PNG up to 10x10, 100x100, etc. Whatever makes sense on your page. (I used a 200x200 PNG and it was only 0.25 kb, so there's no real concern over file size here.)

After visiting this post, I created my web page with 3, 1x1 PNGs with varying transparency.

Dreamweaver CS5 was tanking. I was having flash backs to DOS!!! Apparently any time I tried to scroll, insert text, basically do anything, DW was trying to reload the semi transparent areas 1x1 pixel at a time ... YIKES!

Adobe tech support didn't even know what the problem was, but told me to rebuild the file (it worked on their systems, incidentally). It was only when I loaded the first transparent PNG into the css file that the doc dove deep again.

Then I found a post on another help site about PNGs crashing Dreamweaver. Size your PNG up; there's no downside to doing so.