pip install textual

pip install textual-dev

python -m textual

from time import monotonic
from textual.app import App, ComposeResult
from textual.containers import ScrollableContainer
from textual.reactive import reactive
from textual.widgets import Button, Footer, Header, Static
class TimeDisplay(Static):
    """A widget to display elapsed time."""
    start_time = reactive(monotonic)
    time = reactive(0.0)
    total = reactive(0.0)
    def on_mount(self) -> None:
        """Event handler called when widget is added to the app."""
        self.update_timer = self.set_interval(1 / 60, self.update_time, pause=True)
    def update_time(self) -> None:
        """Method to update time to current."""
        self.time = self.total + (monotonic() - self.start_time)
    def watch_time(self, time: float) -> None:
        """Called when the time attribute changes."""
        minutes, seconds = divmod(time, 60)
        hours, minutes = divmod(minutes, 60)
        self.update(f"{hours:02,.0f}:{minutes:02.0f}:{seconds:05.2f}")
    def start(self) -> None:
        """Method to start (or resume) time updating."""
        self.start_time = monotonic()
        self.update_timer.resume()
    def stop(self) -> None:
        """Method to stop the time display updating."""
        self.update_timer.pause()
        self.total += monotonic() - self.start_time
        self.time = self.total
    def reset(self) -> None:
        """Method to reset the time display to zero."""
        self.total = 0
        self.time = 0
class Stopwatch(Static):
    """A stopwatch widget."""
    def on_button_pressed(self, event: Button.Pressed) -> None:
        """Event handler called when a button is pressed."""
        button_id = event.button.id
        time_display = self.query_one(TimeDisplay)
        if button_id == "start":
            time_display.start()
            self.add_class("started")
        elif button_id == "stop":
            time_display.stop()
            self.remove_class("started")
        elif button_id == "reset":
            time_display.reset()
    def compose(self) -> ComposeResult:
        """Create child widgets of a stopwatch."""
        yield Button("Start", id="start", variant="success")
        yield Button("Stop", id="stop", variant="error")
        yield Button("Reset", id="reset")
        yield TimeDisplay()
class StopwatchApp(App):
    """A Textual app to manage stopwatches."""
    CSS_PATH = "test3.tcss"
    BINDINGS = [("d", "toggle_dark", "Toggle dark mode")]
    def compose(self) -> ComposeResult:
        """Called to add widgets to the app."""
        yield Header()
        yield Footer()
        yield ScrollableContainer(Stopwatch(), Stopwatch(), Stopwatch())
    def action_toggle_dark(self) -> None:
        """An action to toggle dark mode."""
        self.dark = not self.dark
if __name__ == "__main__":
    app = StopwatchApp()
    app.run()

Stopwatch {
    layout: horizontal;
    background: $boost;
    height: 5;
    margin: 1;
    min-width: 50;
    padding: 1;
}
TimeDisplay {
    content-align: center middle;
    text-opacity: 60%;
    height: 3;
}
Button {
    width: 16;
}
#start {
    dock: left;
}
#stop {
    dock: left;
    display: none;
}
#reset {
    dock: right;
}
.started {
    text-style: bold;
    background: $success;
    color: $text;
}
.started TimeDisplay {
    text-opacity: 100%;
}
.started #start {
    display: none
}
.started #stop {
    display: block
}
.started #reset {
    visibility: hidden
}