Unexpected white area below html in Reactjs - reactjs

Question

I use Reactjs and encounter an unexpected white area below the html tag:
I've checked all my .css files and cannot find any margin, padding or position attributes that might cause that problem. When I use Google Chrome inspector, I cannot inspect that white space since it's below my html tag (image above). There's no error messages indicate the cause.
My react app structure:
Here's the code:
App.js:
import React, {Component} from 'react';
import Wrapper from './components/Wrapper';
import SongCard from './components/SongCard';
import songs from './songs.json';
class App extends Component {
state = {
songs
};
render() {
return ([
<div key={0}>
<Wrapper>
{this.state.songs.map(song => (
<SongCard
key={song.id}
id={song.id}
name={song.name}
artist={song.artist}
src={song.src}
/>
))}
</Wrapper>
</div>
]);
}
}
export default App;
Wrapper.js:
import React from 'react';
import './Wrapper.css';
const Wrapper = props => (
<div className="row justify-content-center">
<div className="col-lg-8">{props.children}</div>
</div>
);
export default Wrapper;
Wrapper.css:
.row, .col-lg-8 {
margin: 0;
padding: 0;
color: white;
font-family: 'Amaranth', sans-serif;
}
SongCard.js:
import React from 'react';
import './SongCard.css';
const SongCard = props => (
<div className="song-card">
<div className="row">
<div className="col-auto spotify-player">
<iframe title={props.id} src={props.src} frameBorder="0" allowtransparency="true"></iframe>
</div>
<div className="col text-center song-info">
<div>{props.name}</div>
<div>{props.artist}</div>
</div>
</div>
<div className="song-card-divider"></div>
</div>
);
export default SongCard;
SongCard.css:
iframe {
width: 100%;
}
.col, .col-auto, .song-card {
margin: 0;
padding: 0;
background-color: #343a40;
}
.spotify-player {
width: 80px;
height: 80px;
}
.song-card-divider {
height: 0;
border-top: 1px solid #e9ecef;
}
I've looked for answers but couldn't find any answer.

Answer 1

I've found the cause of the problem:
It's the iframe height that causes the extra white area on the bottom of the page. I post my answer here so this question can be marked as answered and hopefully it helps people who have the same problem.