Hi, I figured it out! So the theme is basically GitHub Dark Default with a few customizations. To add the customizations, you have to open up settings.json and add a few things.
Step 1: Set the theme to GitHub Dark Default.
Step 2: Press Ctrl + Shift + P and then type Preferences: Open Settings (JSON)
Step 3: Scroll down until you find workbench.colorCustomizations and then inside that you should paste this:
"[GitHub Dark Default]": { // This is CS50 style :)
"activityBar.background": "#000",
"editor.background": "#000",