Navigate to chrome://flags, find Developer Tools Experiments and toggle to Enabled.
Reload Chrome.
In DevTools, click the three dots menu, go to Settings -> Experiments and select Allow UI Themes.
Set theme to Dark Mode (this is important, or the theme won't look right).
To set theme to Dark Mode, go to Preferences(In DevTools settings itself) -> Appearance -> Theme and select Dark.
Load a new tab and enjoy your awesome new DevTools theme!