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",
"editor.lineHighlightBackground": "#0000",
"editor.lineHighlightBorder": "#0000",
"editorWhitespace.foreground": "#59A5FC",
"sideBar.background": "#000000",
"terminal.foreground": "#fff",
"terminal.background": "#000000",
"editorGroup.border": "#000000",
"tab.border": "#424242",
"panel.border": "#424242",
"terminal.border": "#000",
"sideBar.border": "#000",
"titleBar.border": "#000",
"tab.activeBorder": "#000",
"editorGroupHeader.tabsBorder": "#424242",
"editorGroupHeader.tabsBackground": "#000000",
"tab.activeBackground": "#000000",
"tab.activeBorderTop": "#ff0000",
"panelTitle.activeBorder": "#ff0000",
"titleBar.activeBackground": "#000000",
"panel.background": "#000000",
},
Step 4: Double-check to make sure it looks like this:
Credits to u/WinXPbootsup and u/Dhananjayyy on Reddit.