add(container/rectangle): add content creation

src/style.zig

@@ -66,10 +66,6 @@ pub fn value(this: Style, writer: anytype, cp: u21) !void {
     try std.fmt.format(writer, "m", .{});
     // content
     try std.fmt.format(writer, "{s}", .{buffer});
-    // TODO: is it necessary to reset the graphics mode afterwards to ensure
-    // that everything rendered behind is still as expected (without any
-    // side-effects)?
-    // try writer.print("\x1b[0m", .{});
 }
 
 // TODO: implement helper functions for terminal capabilities: