Change font (and wording) in child theme storefront

Hi. I’m new to WordPress, and I have a little experience of HTML but not much with CSS, so I’m trying to teach myself a bit. I have learned about hooks (and believe I understand action hooks at least). So in order to keep the learning curve going I want to learn how to change the text of “Cart Totals” on my cart page https://3c9.42b.myftpupload.com. I have created a child theme and tried changing the wording, but with no success at all. I thought I should use a filter hook for this but it seems there is no hook for it. So I decided to at least begin my education by changing the font color of the words “Cart Totals”. I noted that there is a class “cart_totals ” class so I added the following code to my child style.css:
.cart_totals {
text-color: red;
}
Nothing changes at all. Obviously I have made a syntax error or forgotten something here, but I can’t work out what. I believe it must be something simple, so I apologise in advance for the “dumb” question. Please help.