Serve Google Fonts from Key CDN

Thanks Mike
Sorry to be a dummy but that is a little over my technical prowess!
I have some CSS but I do not know where to put it or even if it will work.
I have a fonts folder in the root directory and have this (an example for Lato font) as the base CSS with CDN location but I do not know how to tell the theme to go there for fonts instead of calling the Google servers.

The Lato example CSS:

/* lato-300 - latin */
@font-face {
  font-family: 'Lato';
  font-style: normal;
  font-weight: 300;
  src: url('https://cdn.swarez.co.uk/fonts/lato-v11-latin-300.eot'); /* IE9 Compat Modes */
  src: local('Lato Light'), local('Lato-Light'),
       url('https://cdn.swarez.co.uk/fonts/lato-v11-latin-300.eot?#iefix') format('embedded-opentype'), /* IE6-IE8 */
       url('https://cdn.swarez.co.uk/fonts/lato-v11-latin-300.woff2') format('woff2'), /* Super Modern Browsers */
       url('https://cdn.swarez.co.uk/fonts/lato-v11-latin-300.woff') format('woff'), /* Modern Browsers */
       url('https://cdn.swarez.co.uk/fonts/lato-v11-latin-300.ttf') format('truetype'), /* Safari, Android, iOS */
       url('https://cdn.swarez.co.uk/fonts/lato-v11-latin-300.svg#Lato') format('svg'); /* Legacy iOS */
}

Any help is appreciated.
Regards
Ed

I appreciate all your help Mike.
I now find the problem being that I also use Oswald for all the headers and titles etc.
Essentially the theme is using these two fonts in the Options which is great for all the page styling – and that’s how i want to keep it.
However, now I have added the CSS and the code you kindly gave me I only have Oswald or Lato and not both. Additionally there is no weighting for things like Special Headings which are different when i use the theme options rather than putting in my own CSS.

Is there any way the theme can simply be told to replace the source of the fonts from Google API’s to my CDN? The way this is right now is stripping away all the styling…. I am struggling I admit… Sorry Mike – I am very grateful for your help
Best
Ed

Thanks Mike
I still can’t get this to work properly but thanks for trying anyway.
Regards
Ed