CSS styling cannot be applied when using Flask

Question

So, I ran my web page with Flask. It worked fine, but once I run my web page through Flask, I cannot seem to apply new styling to it.

<link rel="stylesheet" type="text/css" href="{{ url_for('static', filename='style.css') }}">

At first, my stylesheet contained the following code;

html,body{
  padding: 0%;
  margin: 0%;
  background-color: #67030d;
}
.main{
  background-color: #67030d;  
  box-sizing: border-box;
}

The next changes that I did were;

html,body{
  padding: 0%;
  margin: 0%;
}
.main{
  background-color: #67030d;  
  box-sizing: border-box;
}

After running with the newly made changes, I still had the color applied to my entire HTML and body tag.

When I inspect the webpage, it shows that the color has been applied to the HTML and body tag.

This is the issue I am facing in Google Chrome but not in Firefox. How do I solve this?

My apologies if I am not clear.

Thank you in advance!