Format whole background for code blocks

Author: VAWVAW

src/message/html.rs

@@ -366,7 +366,9 @@ impl StyleTreeNode {
             },
             StyleTreeNode::Code(child, _) => {
                 let style = style.bg(Color::Indexed(236));
+                let old = printer.set_base_style(style);
                 child.print(printer, style);
+                printer.set_base_style(old);
             },
             StyleTreeNode::Header(child, level) => {
                 let style = style.add_modifier(StyleModifier::BOLD);

src/message/printer.rs

@@ -92,6 +92,11 @@ impl<'a> TextPrinter<'a> {
         self.width
     }
 
+    /// Sets the base style and returns the old style
+    pub fn set_base_style(&mut self, new: Style) -> Style {
+        std::mem::replace(&mut self.base_style, new)
+    }
+
     /// Create a new printer with a smaller width.
     pub fn sub(&self, indent: usize) -> Self {
         TextPrinter {