How can you change Quark theme default colors?

Hi,
I've read through the documentation about themes, I've created a MyTheme based on Quark and now I'd like to change the primary and secondary colors that are set as variables in the Spectre CSS. However, my site is on shared hosting and I'm not sure I can access to it through SSH and rebuild the compiled CSS from the SCSS files.

What would be the best way to change those colors?

I understand I need to change variables values in user/themes/quark/scss/spectre/_variables.scss, precisely $primary-color: #3085EE !default; and $dark-color: #454d5d !default;
And after that? How should I compile the CSS files again? Is this something that can be done from within Grav?

If I can't go along that route, what's the alternative? Searching for all the occurrences of #3085EE and #454d5d and add new references in custom.css?

TIA
Marco

On shared hosting a provider will not let you compile Sass...

Compiling Sass and any other development/testing/debugging should be done on your local installation. When you're done, you upload the results to the production server using github, FTP or cPanel, or ...

For a side project like this, I'd like to avoid installing npm, gulp, etc. On top of that, I'm working from different locations, that's why I chose to work on a remote test server, not on a local one.