Style Rules Don’t Work in styles.css

Hi.

I’m currently building a website using Twenty Twenty-Four, and I’m unable to get a custom style rule to work in the main stylesheet, styles.css.

When I use Google Chrome’s developer tools to insert a style rule for testing, it works. But when I actually insert the rule in styles.css, it doesn’t work.

I’m trying to add the following rule for the footer:

footer.wp-block-template-part {
margin: 0;
}

The purpose is to remove the margin that was applied by the following rule from theme.json:

:where(.wp-site-blocks) > * {
margin-block-start: 1.2rem;
margin-block-end: 0;
}

Any help that you could give me would be much-appreciated. Like I said, new style rules added to styles.css don’t work.

Glenn