[Fixed]-Why is django displaying white lite on top of the page when using bootstrap

django displays a white line on top

This has nothing to do with Django. It’s a CSS issue.

You wrote this:

.page-header {
    background-color: #ff9400;
    margin-top: 0;
    padding-top: 0;
    padding: 20px 20px 20px 40px;
}

The last line overwrite padding-top with 20px. Replace your CSS with:

.page-header {
    background-color: #ff9400;
    margin-top: 0;
    padding: 0 20px 20px 40px;
}

When I just double click my html file to open it in the browser it
looks fine, but when I start my server via django, it doesn’t look
good.

That’s probably because your custom CSS isn’t loaded when you just open the HTML file. Your browser cannot read {% static "css/blog.css" %}.