Without seeing your code, it's impossible to guess what may be going on.
1. Copy & paste the following code into a new, blank document and save to your local site folder as test.html.
This document contains embedded CSS styles and an inline style on the Column 2 <div>.

2. Attempt to change any or all of the CSS values.
3. Save document (Ctrl/Cmd+S) and refresh screen (F5).
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Flexbox Columns</title>
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
body {
margin: 0;
padding: 0;
background:antiquewhite;
color:brown;
text-align: center;
}
nav {
background-color:tan;
padding:2%;
border-top:1px solid brown;
}
nav a {color:purple;}
/* Mobile first*/
.flexbox-container {
display: flex;
flex-direction: column;
}
/* Tablets, Desktops*/
@media only screen and (min-width: 630px) {
.flexbox-container {
flex-direction: row;
justify-content: space-evenly;
}
}
/* All devices */
.flexbox-container > div {
flex-grow: 1;
padding: 5%;
background-color:brown;
color:antiquewhite;
}
img {
max-width: 100%;
height: auto;
display: block;
vertical-align: baseline;
margin: 0 auto;
}
</style>
</head>
<body>
<header>
<h1>XYZ Website</h1>
<h2>Lorem ipsum dolor</h2>
</header>
<nav><a href="#">Navigation Link</a></nav>
<main class="flexbox-container">
<div>
<h3>Column 1</h3>
<img src="https://dummyimage.com/300x227" alt="placeholder">
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Omnis id in commodi dicta fuga sit, consequuntur.</p>
</div>
<div style="background-color:navajowhite; color:brown">
<h3>Column 2</h3>
<img src="https://dummyimage.com/300x227" alt="placeholder">
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Omnis id in commodi dicta fuga sit, consequuntur.</p>
</div>
<div>
<h3>Column 3</h3>
<img src="https://dummyimage.com/300x227" alt="placeholder">
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Omnis id in commodi dicta fuga sit, consequuntur.</p>
</div>
</main><!--/flex-container-->
<footer> <small>© 2020 XYZ Website all rights reserved.</small>
</footer>
</body>
</html>
Do you see your style changes?