One element is transparents, and second no

[tomi0001]

I would line that main element about id = #menu_gorne was not transparetnts and so is, but i apply for second elementu value opacity: none and it is trasnparents and not should.

body {
  
 

  
  
  
 background-image: url('./cardboard.png'); /* from http://subtlepatterns.com */ 
}

#menu_gorne {
    width: 80%;
    background-color: red;
    height: 60px;
    margin-left: auto; 
    margin-right: auto;
    opacity: 0.7;
    vertical-align: middle;
    line-height: 40px;
    border-radius: 29px;
    position: relative;
    

}

.pozycja {
 
    position: absolute;
    top:15%;
    opacity: none;
    text-align: center;
    display:table-cell;
    width: 120px;
 
    border-radius: 29px;
    
    
}

.d {
    
    background-color: green;   
    
}


<br><br>
<div id="menu_gorne">
    <div class="pozycja">
        <div class="d">sss</div>
    </div>
    
    
</div>

[Erik_J]

Hi tomi0001, welcome to the forum.

I don’t umderstand your question.

Maybe you could check what values are allowed for that property (0-1) and what it does:

opacity - CSS: Cascading Style Sheets | MDN

[tomi0001]

Thanks the solution was
background-color: rgba(255,0,0,0.7);