CSS File for Settings/Customizer Fields

Hey there! I'm unclear about how to best use Settings Pages/Customizer Pages to change the CSS for Beaver Builder.

For example, I have fields that I want to apply to default Beaver Builder button colors. How can I create a my-css-styles.php file where I can use these values? I couldn't find an example or tutorial on how to use settings pages fields to create a file like this.

Basically what I'm trying to do is something like:

.fl-button: {
    color: echo rwmb_meta( 'fm_primary_button_text_color' );
    background-color: echo rwmb_meta( 'fm_primary_button_color' );
}