Spectrum uses Adobe’s brand font, Adobe Clean.
Adobe Clean is Spectrum’s primary typeface. It's used for Latin-based languages as well as Greek and Cyrillic scripts.
Adobe Clean Serif is a companion font family to Adobe Clean. It covers most Latin-based languages as well as Cyrillic alphabets and Greek.
Adobe Clean Han is a companion font family to Adobe Clean. It is used for Simplified Chinese, Traditional Chinese, Japanese, and Korean.
Source Code Pro is used to display code snippets, either inline with another typeface or as a standalone block.