[gatsby-theme-minimal-blog] I can't toggle between light mode and dark mode.

[dev-hobin]

i just clone gatsby-theme-minimal-blog template and run yarn develop.
and I click the toggle button on the top right to change the color theme, but the color theme hasn't changed..
but when I refreshed the page the changed color theme was applied.
why doesn't the theme change immediately when I press the toggle button?
I think this is an easy problem, but I've spent quite a bit of time and haven't found the cause yet.