Increase performance of applying dark theme on new page loads

Basic test: login as any user select dark theme navigate around sakai notice if dark theme is applied instantly or whether there is a slight delay before it is applied. Test of OS dark mode detection: set your local operating system to use dark mode go to Sakai ensure the Gateway appears dark before you log in log into a new account that you've never logged into Sakai before (the Tutorial should appear automatically) ensure Sakai appears in dark theme automatically ensure the Dark Theme toggle (in the account menu) has "On" selected log out set your local operating system off of dark mode go to Sakai in a new browser (or in Private Mode, or clear your browser's cache and history) log into Sakai with the same user as a few steps ago ensure Sakai appears in dark theme automatically still Test of various combinations of dark and light modes: ensure logging into the same Sakai account on various browsers keeps the last setting of the Dark Theme setting for that user (test with both Dark Theme toggled on and off) ensure logging into various Sakai accounts on various browsers keeps the last setting of the Dark Theme setting for each user separate of the other users (test with both Dark Theme toggled on and off) (e.g. if you enable Dark Theme on your first user account and disable it on your second user account, ensure the first user still has Dark Theme enabled when you go back to that account after the second account) ensure logging into various Sakai accounts keeps the expected settings for Dark Theme based on the various states of your OS's dark mode (enabled and disabled)