diff --git a/examples/calculator.css b/examples/calculator.css
new file mode 100644
index 000000000..0d777edfa
--- /dev/null
+++ b/examples/calculator.css
@@ -0,0 +1,32 @@
+Screen {
+    overflow: auto;
+}
+
+#calculator {
+    layout: table;
+    table-size: 4;
+    table-gutter: 1 2;
+    table-columns: 1fr;
+    table-rows: 2fr 1fr 1fr 1fr 1fr 1fr;
+    margin: 1 2;
+    min-height:25;  
+    min-width: 26; 
+}
+
+Button {
+    width: 100%;
+    height: 100%;    
+}
+
+#numbers {
+    column-span: 4;
+    content-align: right middle;
+    padding: 0 1;
+    height: 100%;
+    background: $primary-lighten-2;
+    color: $text-primary-lighten-2;
+}
+
+#number-0 {
+    column-span: 2;
+}
diff --git a/examples/calculator.py b/examples/calculator.py
new file mode 100644
index 000000000..7c06c4d54
--- /dev/null
+++ b/examples/calculator.py
@@ -0,0 +1,142 @@
+from decimal import Decimal
+
+from textual.app import App, ComposeResult
+from textual import events
+from textual.layout import Container
+from textual.reactive import Reactive
+from textual.widgets import Button, Static
+
+
+class CalculatorApp(App):
+    """A working 'desktop' calculator."""
+
+    numbers = Reactive.var("0")
+    show_ac = Reactive.var(True)
+    left = Reactive.var(Decimal("0"))
+    right = Reactive.var(Decimal("0"))
+    value = Reactive.var("")
+    operator = Reactive.var("plus")
+
+    KEY_MAP = {
+        "+": "plus",
+        "-": "minus",
+        ".": "point",
+        "*": "multiply",
+        "/": "divide",
+        "_": "plus-minus",
+        "%": "percent",
+        "=": "equals",
+    }
+
+    def watch_numbers(self, value: str) -> None:
+        """Called when numbers is updated."""
+        # Update the Numbers widget
+        self.query_one("#numbers", Static).update(value)
+
+    def compute_show_ac(self) -> bool:
+        """Compute switch to show AC or C button"""
+        return self.value in ("", "0") and self.numbers == "0"
+
+    def watch_show_ac(self, show_ac: bool) -> None:
+        """Called when show_ac changes."""
+        self.query_one("#c").display = not show_ac
+        self.query_one("#ac").display = show_ac
+
+    def compose(self) -> ComposeResult:
+        """Add our buttons."""
+        yield Container(
+            Static(id="numbers"),
+            Button("AC", id="ac", variant="primary"),
+            Button("C", id="c", variant="primary"),
+            Button("+/-", id="plus-minus", variant="primary"),
+            Button("%", id="percent", variant="primary"),
+            Button("÷", id="divide", variant="warning"),
+            Button("7", id="number-7"),
+            Button("8", id="number-8"),
+            Button("9", id="number-9"),
+            Button("×", id="multiply", variant="warning"),
+            Button("4", id="number-4"),
+            Button("5", id="number-5"),
+            Button("6", id="number-6"),
+            Button("-", id="minus", variant="warning"),
+            Button("1", id="number-1"),
+            Button("2", id="number-2"),
+            Button("3", id="number-3"),
+            Button("+", id="plus", variant="warning"),
+            Button("0", id="number-0"),
+            Button(".", id="point"),
+            Button("=", id="equals", variant="warning"),
+            id="calculator",
+        )
+
+    def on_key(self, event: events.Key) -> None:
+        """Called when the user presses a key."""
+
+        def press(button_id: str) -> None:
+            self.query_one(f"#{button_id}", Button).press()
+            self.set_focus(None)
+
+        key = event.key
+        if key.isdecimal():
+            press(f"number-{key}")
+        elif key == "c":
+            press("c")
+            press("ac")
+        elif key in self.KEY_MAP:
+            press(self.KEY_MAP[key])
+
+    def on_button_pressed(self, event: Button.Pressed) -> None:
+        """Called when a button is pressed."""
+
+        button_id = event.button.id
+        assert button_id is not None
+
+        self.bell()  # Terminal bell
+
+        def do_math() -> None:
+            """Does the math: LEFT OPERATOR RIGHT"""
+            try:
+                if self.operator == "plus":
+                    self.left += self.right
+                elif self.operator == "minus":
+                    self.left -= self.right
+                elif self.operator == "divide":
+                    self.left /= self.right
+                elif self.operator == "multiply":
+                    self.left *= self.right
+                self.numbers = str(self.left)
+                self.value = ""
+            except Exception:
+                self.numbers = "Error"
+
+        if button_id.startswith("number-"):
+            number = button_id.partition("-")[-1]
+            self.numbers = self.value = self.value.lstrip("0") + number
+        elif button_id == "plus-minus":
+            self.numbers = self.value = str(Decimal(self.value or "0") * -1)
+        elif button_id == "percent":
+            self.numbers = self.value = str(Decimal(self.value or "0") / Decimal(100))
+        elif button_id == "point":
+            if "." not in self.value:
+                self.numbers = self.value = (self.value or "0") + "."
+        elif button_id == "ac":
+            self.value = ""
+            self.left = self.right = Decimal(0)
+            self.operator = "plus"
+            self.numbers = "0"
+        elif button_id == "c":
+            self.value = ""
+            self.numbers = "0"
+        elif button_id in ("plus", "minus", "divide", "multiply"):
+            self.right = Decimal(self.value or "0")
+            do_math()
+            self.operator = button_id
+        elif button_id == "equals":
+            if self.value:
+                self.right = Decimal(self.value)
+            do_math()
+
+
+app = CalculatorApp(css_path="calculator.css")
+if __name__ == "__main__":
+    app.run()
diff --git a/src/textual/css/query.py b/src/textual/css/query.py
index 9b8c6b96a..202a0767a 100644
--- a/src/textual/css/query.py
+++ b/src/textual/css/query.py
@@ -251,6 +251,19 @@ class DOMQuery:
                 if isinstance(node, filter_type):
                     yield node
 
+    def set_class(self, add: bool, *class_names: str) -> DOMQuery:
+        """Set the given class name(s) according to a condition.
+
+        Args:
+            add (bool): Add the classes if True, otherwise remove them.
+
+        Returns:
+            DOMQuery: Self.
+        """
+        for node in self:
+            node.set_class(add, *class_names)
+        return self
+
     def add_class(self, *class_names: str) -> DOMQuery:
         """Add the given class name(s) to nodes."""
         for node in self:
diff --git a/src/textual/dom.py b/src/textual/dom.py
index 984ac8f16..a79058e78 100644
--- a/src/textual/dom.py
+++ b/src/textual/dom.py
@@ -705,6 +705,17 @@ class DOMNode(MessagePump):
         """
         return self._classes.issuperset(class_names)
 
+    def set_class(self, add: bool, *class_names: str) -> None:
+        """Add or remove class(es) based on a condition.
+
+        Args:
+            add (bool):  Add the classes if True, otherwise remove them.
+        """
+        if add:
+            self.add_class(*class_names)
+        else:
+            self.remove_class(*class_names)
+
     def add_class(self, *class_names: str) -> None:
         """Add class names to this Node.
 
diff --git a/src/textual/reactive.py b/src/textual/reactive.py
index dcc9757c3..99dea0ea0 100644
--- a/src/textual/reactive.py
+++ b/src/textual/reactive.py
@@ -74,6 +74,21 @@ class Reactive(Generic[ReactiveType]):
         """
         return cls(default, layout=layout, repaint=repaint, init=True)
 
+    @classmethod
+    def var(
+        cls,
+        default: ReactiveType | Callable[[], ReactiveType],
+    ) -> Reactive:
+        """A reactive variable that doesn't update or layout.
+
+        Args:
+            default (ReactiveType | Callable[[], ReactiveType]):  A default value or callable that returns a default.
+
+        Returns:
+            Reactive: A Reactive descriptor.
+        """
+        return cls(default, layout=False, repaint=False, init=True)
+
     @classmethod
     async def initialize_object(cls, obj: object) -> None:
         """Call any watchers / computes for the first time.
diff --git a/src/textual/widgets/_button.py b/src/textual/widgets/_button.py
index 4a2b806b2..3121ef9c4 100644
--- a/src/textual/widgets/_button.py
+++ b/src/textual/widgets/_button.py
@@ -18,8 +18,8 @@ from ..message import Message
 from ..reactive import Reactive
 from ..widget import Widget
 
-ButtonVariant = Literal["default", "success", "warning", "error"]
-_VALID_BUTTON_VARIANTS = {"default", "success", "warning", "error"}
+ButtonVariant = Literal["default", "primary", "success", "warning", "error"]
+_VALID_BUTTON_VARIANTS = {"default", "primary", "success", "warning", "error"}
 
 
 class InvalidButtonVariant(Exception):
@@ -57,6 +57,29 @@ class Button(Widget, can_focus=True):
         background: $panel;
         border-bottom: tall $panel-lighten-2;
         border-top: tall $panel-darken-2;                
+        tint: $background 30%;
+    }
+
+    /* Primary variant */
+    Button.-primary {
+        background: $primary;
+        color: $text-primary;
+        border-top: tall $primary-lighten-3;
+        border-bottom: tall $primary-darken-3;
+      
+    }
+
+    Button.-primary:hover {
+        background: $primary-darken-2;
+        color: $text-primary-darken-2;
+
+    }
+
+    Button.-primary.-active {
+        background: $primary;
+        border-bottom: tall $primary-lighten-3;
+        border-top: tall $primary-darken-3;
+    
     }
 
 
@@ -188,14 +211,18 @@ class Button(Widget, can_focus=True):
         label.stylize(self.text_style)
         return label
 
-    async def on_click(self, event: events.Click) -> None:
+    async def _on_click(self, event: events.Click) -> None:
         event.stop()
-        if self.disabled:
+        self.press()
+
+    def press(self) -> None:
+        """Respond to a button press."""
+        if self.disabled or not self.display:
             return
         # Manage the "active" effect:
         self._start_active_affect()
         # ...and let other components know that we've just been clicked:
-        await self.emit(Button.Pressed(self))
+        self.emit_no_wait(Button.Pressed(self))
 
     def _start_active_affect(self) -> None:
         """Start a small animation to show the button was clicked."""
@@ -204,7 +231,7 @@ class Button(Widget, can_focus=True):
             self.ACTIVE_EFFECT_DURATION, partial(self.remove_class, "-active")
         )
 
-    async def on_key(self, event: events.Key) -> None:
+    async def _on_key(self, event: events.Key) -> None:
         if event.key == "enter" and not self.disabled:
             self._start_active_affect()
             await self.emit(Button.Pressed(self))