Dark/Light Theme

[je-poy]

1. Add something like light & dark mode. This dark mode is implemented by adding a dark layer above the image when activated, preferably using nord0 or similar color, while the light mode is removing (or just changing the opacity to 0) the darkener layer. I choose to use Nord theme since we are in-line with what Nord theme provides. Nord theme is basically a set of color palette with arctic & north-bluish theme (maybe we need to put some information about it as well in the README.md. Winterly Tab & Nord theme would be a very icy & good match. More about Nord theme can be read in nordtheme.com.
2. For the light and dark mode, we can use the device default theme as the default winter tab theme. A toggle button would be also good for switching between themes.