Fix embed bug and update dark mode appearance

[Frozen-H2O]

• Fix embed duration caluculation being off
• Rework how dark mode works, where we simply apply .theme-dark to the html of the page, then overwrite variables in css instead of using django conditionals
• Update jquery
• Use blue accent on both dark and light modes

Theme configs are in main.css's :root and .theme-dark if they need to be changed.