Styling for QR Code using theme framework

style/src/qr_code.rs

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+//! Change the appearance of a QR code.
+use crate::core::Color;
+
+/// The appearance of a QR code.
+#[derive(Debug, Clone, Copy)]
+pub struct Appearance {
+    /// The color of the QR code data cells
+    pub cell: Color,
+    /// The color of the QR code background
+    pub background: Color,
+}
+
+/// A set of rules that dictate the style of a QR code.
+pub trait StyleSheet {
+    /// The supported style of the [`StyleSheet`].
+    type Style: Default;
+
+    /// Produces the style of a QR code.
+    fn appearance(&self, style: &Self::Style) -> Appearance;
+}