How to change background colors for child templates in Jinja?

Solution

@application.before_request
def before_request_func():
    g.BODY_COLOR = "bg-red"

body {
  font-family: "Montserrat", sans-serif;
  background-color: --body-color;
}

@application.route('/')
def index():
    b_c = "bg-red"
    retun render_template('index.html',b_c=b_c)

body {
  font-family: "Montserrat", sans-serif;
  background-color: --body-color;
}