align: center middle only aligns on horizontal axis

[darrenburns]

Application code:

from textual.app import App, ComposeResult
from textual.widgets import Static

class JustABox(App):
    def compose(self) -> ComposeResult:
        yield Static("Hello, World!", id="box")

if __name__ == '__main__':
    app = JustABox(css_path="just_a_box.css", watch_css=True)
    app.run()

CSS:

Screen {
    layout: dock;
    height: 100%;
}

#box {
    height: 50%;
    width: 50%;
    align: center middle;
    background: green;
}

Result: