I can't modify the .yml file

Hi, I wrote the following in config.yml:

- name: theme
    label: Theme
    editor:
      preview: false
    files:
      - file: _data/theme.yml
        label: Styling
        name: styling
        fields:
          - {
              label: Main Background Color,
              name: bgcolor,
              widget: string,
              required: false,
            }
          - {
              label: Landing Button Color,
              name: landingbuttoncolor,
              widget: string,
              required: false,
            }

and _data/theme.yml:

bgcolor: "#10121a"
landingbuttoncolor: "#202833"

I write the variables from the admin panel and press the Publish button. It says “Entry saved” but when I go back to _data/theme.yml I see that nothing has changed. So what did I do wrong? Thanks

EDIT: WHEN I PUSHED THE CODE INTO GITHUB, IT SAID INCOMING CHANGES

Netlify CMS is a git based CMS. All changes you make will automatically be pushed to your repo. If you want to make changes locally without pushing every change, which I assume is what you’re trying to do, check out this feature: