ODIN ADMIN ships with a light content area and a dark sidebar. It doesn't include a ready-made dark theme or a theme switch.
Because colours are CSS variables, you can add one yourself: put the dark values in css/custom.css under an attribute and set it on <html>:
[data-theme="dark"] {
--body-bg: #0F172A;
--card-bg: #1E293B;
--text: #E2E8F0;
--border: rgba(255, 255, 255, .08);
}Check css/base/variables.css for the exact variable names, and test charts and plugin themes (in css/vendor/), which use some fixed colours. A small script can toggle the attribute and remember the choice in localStorage.