S. + Style

s_style.rs

trait StyleTrait: Sized {
    fn font_size(self, font_size: u32) -> Style {
        Style::default().font_size(font_size)
    }
    fn height(self, height: u32) -> Style {
        Style::default().height(height)
    }
}

struct S;
impl StyleTrait for S {}

#[derive(Default, Debug)]
struct Style {
    font_size: u32,
    height: u32,
}

impl StyleTrait for Style {
    fn font_size(mut self, font_size: u32) -> Style {
        self.font_size = font_size;
        self
    }
    fn height(mut self, height: u32) -> Style {
        self.height = height;
        self
    }
}

fn main() {
    let style = S.font_size(16).height(50);
    dbg!(style);
}

Runnable in https://play.rust-lang.org/