CSS adjust brightness of image background and not content - html

Question

The section has a background image with content on top.
I want to decrease the brightness of only the background image in the section and not the content.
I have tried the below, however, the brightness still applies to all and not just the image.
<!-- Section -->
<div id="section1">
<div id="content">
<h1 class="heading">headline text</h1>
<h4 class="subHeading"> Sub-headline text</h4>
<!-- Call to action button -->
<br><br>
<button> Join our wait list </button>
</div>
#section1 {
background: url('../images/headerimage1.jpg') center center no-repeat;
background-size: cover;
-webkit-filter: brightness(0.5);
filter: brightness(0.5);
padding-top: 100px;
padding-bottom: 100px;
padding-left: 10%;
padding-right: 10%;
color: white;
text-align: center;
}
#content {
-webkit-filter: brightness(1);
filter: brightness(1);
}

Answer 1

You can add a new element of transparent black that overlays just the background, with the contents of your div sitting in front of it.
<div id="section1">
<div id="content">
</div>
</div>
CSS:
#section1 {
background: url('../images/headerimage1.jpg') center center no-repeat;
background-size: cover;
position: relative;
}
#content {
position: absolute;
}
#section1::before {
content: '';
display: block;
position: absolute;
background-color: #000;
opacity: 0.5;
width: 100%;
height: 100%;
}