Why isn't the div's background image showing up behind child elements in my React app?

I want to apply a background image to a div, but the divs' child element does not show the background image behind it. The image is only shown in the blank space. I'm using ReactJS.

Here is what's showing up:

Here is the code for the div

 
<div className='start'>
	<Navbar/>
	<div className='firstContainer'>
		<h3 className="subheading-div1">
            Experience limitless charging possibilities with Charzit
          </h3>
		<h1 className="home-heading">
			<span>EV Charging</span>
			<span className="greenText"> Solutions </span>
			<span>Where you like it </span>
		</h1>
		<p className="desc-div1">
            Our electric vehicle charging solutions are adaptable and efficient
            , allowing businesses to fulfill the rising demand for clean energy
            transportation while lowering their CO2 footprint.
          </p>
		<h2 className="desc-div1">Download Now</h2>
		<a href="/" target="_blank">
			<div className="btn-div">
				<FaGooglePlay className="btn" />
			</div>
		</a>
		<a href="/" target="_blank">
			<div className="btn-div">
				<FaApple className="btn" />
			</div>
		</a>
	</div>
</div>

CSS

.start {
    height: 100vh;
    background-image: url("../../public/main2.jpg");
    background-size: cover;
    background-size: 100%;
    background-repeat: no-repeat;
}

.firstContainer {
    padding-left: 50px;
    width: 50vw;
    z-index: -1;
}

.subheading-div1 {
    font-size: 1.7rem;
    margin: 0px;
}

.home-heading {
    font-size: 3rem;
    margin: 20px;
    margin-bottom: 0px;
}

.greenText {
    color: #79ca5d;
}

.desc-div1 {
    font-size: 1.4rem;
    font-weight: 700;
    margin-top: 20px;
}

.btn-div {
    background-color: transparent;
    display: inline-block;
    width: 68.46px;
    height: 51.86px;
    border-radius: 5px;
    margin: 20px 20px 0 0;
    border: 1px solid #79ca5d;
}

.btn-div:hover {
    background-color: #79ca5d;
}

.btn {
    color: #fff;
    padding-right: 20px;
    width: 45px;
    height: 45px;
    padding-left: 10px;
    padding-top: 5px;
}

It seems your issue is not reproducible as you have presented it. I've placed it in a snippet below, and it appears to be rendering the way you want.

I would guess that you need to set the background of your .firstContainer element to be transparent. You might have a style somewhere giving it a color.

If you need more help, I recommend updating your question with a snippet that reproduces your issue. If the StackOverflow snippet doesn't work because you require JSX support to make it work, you can use something like CodeSandbox.

<!-- begin snippet: js hide: true console: true babel: false -->

<!-- language: lang-css -->

.start {
    height: 100vh;
    background-image: url("https://kajabi-storefronts-production.kajabi-cdn.com/kajabi-storefronts-production/blogs/18725/images/PuRv7TFRzGdNsmp3iRmj_Tetons.jpg");
    background-size: cover;
    background-size: 100%;
    background-repeat: no-repeat;
}

.firstContainer {
    padding-left: 50px;
    width: 50vw;
    z-index: -1;
}

.subheading-div1 {
    font-size: 1.7rem;
    margin: 0px;
}

.home-heading {
    font-size: 3rem;
    margin: 20px;
    margin-bottom: 0px;
}

.greenText {
    color: #79ca5d;
}

.desc-div1 {
    font-size: 1.4rem;
    font-weight: 700;
    margin-top: 20px;
}

.btn-div {
    background-color: transparent;
    display: inline-block;
    width: 68.46px;
    height: 51.86px;
    border-radius: 5px;
    margin: 20px 20px 0 0;
    border: 1px solid #79ca5d;
}

.btn-div:hover {
    background-color: #79ca5d;
}

.btn {
    color: #fff;
    padding-right: 20px;
    width: 45px;
    height: 45px;
    padding-left: 10px;
    padding-top: 5px;
}

<!-- language: lang-html -->

<div class='start'>
    <div class='firstContainer'>
        <h3 class="subheading-div1">
            Experience limitless charging possibilities with Charzit
          </h3>
        <h1 class="home-heading">
            <span>EV Charging</span>
            <span class="greenText"> Solutions </span>
            <span>Where you like it </span>
        </h1>
        <p class="desc-div1">
            Our electric vehicle charging solutions are adaptable and efficient
            , allowing businesses to fulfill the rising demand for clean energy
            transportation while lowering their CO2 footprint.
          </p>
        <h2 class="desc-div1">Download Now</h2>
        <a href="/" target="_blank">
            <div class="btn-div">
                <FaGooglePlay class="btn" />
            </div>
        </a>
        <a href="/" target="_blank">
            <div class="btn-div">
                <FaApple class="btn" />
            </div>
        </a>
    </div>
</div>

<!-- end snippet -->