So I don't think what you are asking is directly possible, but here's a way to get the effect you are looking for.
Seperate your content from the div that contains the background. Then wrap both of those in a container div and set that div to position: relative;
Now take your content and give it this code:
position: absolute;
top: 0;
left: 0;
Look what I did here:
.bg-img {
background-image: url(https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Ftse3.mm.bing.net%2Fth%3Fid%3DOIP.VKpiZHX8o1MQRM3NLjQaGQHaE8%26pid%3DApi&f=1&ipt=46d3f722b06b0265f5e520392239e52a3b5e8a19f77a81b52fea18d43b5df116&ipo=images);
background-repeat: no-repeat;
background-position: center;
background-size: cover;
height: 250px;
opacity: 0.5;
}
.contain {
position: relative;
}
.contain p {
position: absolute;
top: 0;
left: 0;
}
<div class="contain">
<div class=bg-img></div>
<p> Lorem Ipsum. </p>
</div>