page transition from light to dark when refreshed

[ylw5]

I'd like to use custom theme.
I set variables.css, base.css, and new Layout, use appearance switch button copied from Vue/theme.

.vitepress/theme/index.ts

import './style/index.css'
import Layout from './components/Layout.vue'
export default {
  Layout,
}

Dark mode and switch button work perfectly, but when I refresh page, I can see transition from light to dark, not stay in dark mode.
If I use default theme, page stay in dark if I refresh.
I don't know if I miss something. Anybody can help me?

[ylw5]

I forget adding html.dark {color-scheme: dark;} in variables.css to improve dark mode default style