Dark Mode Persistance

[adam-rozen]

Hello!

I am suggesting saving the dark mode setting to the user's account. This is similar to #1042, but I am posting this as a new Feature Request as that discussion does not show up for some reason when I try to search for it in the GitHub Discussions page.

Currently SimpleLogin seems to just uses a cookie to determine if the site should show in dark mode. This means that dark mode is not synced across devices.

In addition, browsers that clear cookies on exit will have the setting reset every time the browser is quit. A workaround of using the popular Firefox addon Dark Reader does not work, see #1374.

Here is my idea for a basic implementation without changing any UI:

1. When the user logs in, if dark mode is set in the database then set the cookie to true. If dark mode is not set in the database, then do not set the cookie. Dark Mode would only be synced by re-toggling it, but this would keep the solution simple while prevent overriding existing user's dark mode preferences
2. When clicking on the button to switch to dark mode, it should save a value to the database with the user's settings. When switching to bright mode, it should set it to null.

Looking through this repository, I have identified 4 files that I think would need changes:

1. app/models.py - Add a new field to the User model: dark-mode
2. server.py - On login set dark-mode cookie to true if there is a value in the database
3. static/js/theme.js - Add a line before returning for a function that sends a settings API call. Also add the function to send the API call
4. app/api/views/setting.py - Change the settings API to include dark-mode

I can try working on this and have sent an email to the address in the contributing guide to see if it is already being worked on.