How to add custom css styles to WordPress understrap theme?

Question

Themes

Tell me, I have styles from my html template, I tried to enter them everywhere, but there are no changes on the site, the markup works, but the styles do not add custom ones, Please tell me where to enter them, or how to set up a theme for this.
https://github.com/understrap/understrap

Answer 1

understrap/css/theme.css If not applied - look in the Google chrome developer tools, perhaps for this element they are still redefined somewhere. Where exactly - it will be indicated there

Answer 2

In fact, this understrap is some kind of junk!
Installed a child theme. The official instructions and the theme file /understrap-child/sass/child-theme.scss say

// Any additional imported files //
@import "theme/child_theme";  // <--------- Add your styles into this file

I add a piece of code there:

body {
    margin: 0;
    font-family: -apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"Helvetica Neue",Arial,"Noto Sans",sans-serif,"Apple Color Emoji","Segoe UI Emoji","Segoe UI Symbol","Noto Color Emoji";
    font-size: 2rem;
    font-weight: 600;
    line-height: 1.5;
    color: #212529;
    text-align: left;
    background-color: #fff;
}

Nothing really changes. I've been sitting on this understrap for three hours now and I can't do anything