useTheme.ts suggests the way to achieve this is using a "dark-mode" class in the island body, or specifying data-theme=dark in the island tag, but I haven't had any luck with either of those methods.. 
import marimo
__generated_with = "0.7.21-dev18"
app = marimo.App()
@app.cell
def __():
import marimo as mo
return mo,
@app.cell
def __(mo):
mo.md("Hello")
return
@app.cell
def __(mo):
mo.ui.slider(start=0,stop=10,label="slider",show_value=True)
return
@app.cell
def __():
return
if __name__ == "__main__":
app.run()// If it is islands, try a few ways to infer if it is dark mode.
if (isIslands()) {
// If it has a dark mode class on the body, use dark mode.
if (
document.body.classList.contains("dark-mode") ||
document.body.classList.contains("dark")
) {
return "dark";
}
// If it has data-theme=dark or data-mode=dark on the body, use dark mode.
if (
document.body.dataset.theme === "dark" ||
document.body.dataset.mode === "dark" ||
document.body.dataset.vscodeThemeKind === "vscode-dark" ||
document.body.dataset.vscodeThemeKind === "vscode-high-contrast"
) {
return "dark";
}
// We don't want to infer from the system theme,
// since the island consumer may not support dark mode.
return "light";
}#shadow-root the properties are set by the external stylesheet#shadow-root those get overwritten by a constructed stylesheet (presumably you're using something like CSSStyleSheet to inherit styles into the shadow DOM?)mo.ui.slider().style())