Themes

A theme bundles up the look-and-feel decisions of a deck: the color palette, the fonts, the cover style, and the footer defaults for each layout. Instead of setting a dozen properties one by one, a theme gives you a coherent design in a single, reusable file.

The default theme

Every deck starts from the built-in default theme — a light background with the Tachyonn orange (#FF5F1F) as its primary color. You don't have to do anything to get it; it's applied automatically.

(That orange is borrowed from the Brasília sky at dusk — see Where the orange comes from.)

The default theme is itself a plain theme file, default.tt, shipped with Tachyonn. It lists every variable and setting a theme can have, each one commented. That makes it the best starting point for your own theme: copy it and change what you want.

Built-in presets

Besides default, two presets ship inside Tachyonn. Ask for one by name — no file, no path:

===
theme: dark
===

Name	What it is
default	The light theme with the Tachyonn orange. Applied when you say nothing
dark	The same design on a dark blue-grey surface (#12121a), with a slightly lighter orange for contrast and toned-down surfaces for code and panels
physics	A sober deep-blue academic palette plus a TeX macro pack: \R \C \N \Z \Q, \ket \bra \braket \expval, \vb \uv \op \grad \divg \curl \lap, \dd \dv \pdv \order, \abs \norm \unit \qty \ee \ii \kB \degree. Write +[\pdv{f}{x}] or +[\ket{\psi}] with no preamble

Presets are ordinary theme files compiled into the binary: they declare only what differs from default, so everything else (typography, layout variants, footer rules) is inherited. Your deck frontmatter still overrides them key by key, and your own texMacro: lines win over the physics pack on a name clash.

A typo in the name isn't silent: an unknown theme falls back to default and reports a warning in the preview's diagnostics overlay and in the terminal.

Theme files (.tt)

A .tt file ("Tachyonn Theme") holds all your design choices in one place. Put it in the same folder as your .tac file:

my-talk.tac
my-theme.tt

…and point to it from the frontmatter:

===
theme: ./my-theme.tt
===

Anything your file leaves out simply keeps the value from the default theme. So a theme can be as short as a couple of lines — you only override what you want to change.

A minimal example

// my-theme.tt
name: My Theme

accent: #003087
background: #ffffff
headingColor: #003087

That's a complete, valid theme: it changes the accent, background, and heading color, and inherits everything else (fonts, footer behavior, etc.) from the default.

The full picture

The default.tt file is the complete reference — copy it to see every option with comments. Here's the shape of it:

// my-theme.tt
name: My Theme

// ── Colors ──────────────────────────────
accent: #38bdf8           // primary: titles, links, accents
background: #0f172a        // slide background
color: #e2e8f0            // body text
headingColor: #7dd3fc     // slide titles
mutedColor: #64748b       // captions, footer, subtitles
borderColor: #1e293b      // dividers, table rows

// ── Typography ──────────────────────────
font: Inter, sans-serif   // any installed font works; the bundled ones are Atkinson Hyperlegible / Momo Trust Display / JetBrains Mono
fontMono: JetBrains Mono, monospace

// ── Advanced: raw CSS variables ─────────
// Any key starting with -- is passed straight through as a CSS variable.
--tac-code-bg: #1e1e1e
--tac-footer-size: 13px

// ── Cover ───────────────────────────────
coverLayout: title

// ── Footer visibility per layout ────────
footer.title: false
footer.section: false
footer.standard: true
footer.two-column: true
// ... one line per layout

Key reference

This page covers the keys you reach for most often. The complete list — every
key, every synonym, every default — is in the
Property Reference.

Identity and typography

Key	Default	Description
name	default	A display name for the theme (optional).
font / fontSans	Atkinson Hyperlegible, sans-serif	Body font family.
headingFont / titleFont	Momo Trust Display, sans-serif	Titles and headings.
fontMono / fontCode	JetBrains Mono, monospace	Code font family.

Fonts and offline

Atkinson Hyperlegible (body), Momo Trust Display (headings) and JetBrains Mono (code) ship bundled with Tachyonn — self-hosted, never fetched from the internet — so they render identically on every machine, offline. You can name any other font, but it will only appear if the viewer has it installed; otherwise it falls back to a system font.

Colors (friendly names — the same ones you can use in the frontmatter)

Key	CSS variable it sets	Default
accent	--tac-accent	#FF5F1F
background / bg	the slide background	#ffffff
color / textColor	--tac-text	#1c1c28
headingColor / titleColor	--tac-heading	#FF5F1F
mutedColor	--tac-text-muted	#6b7280
borderColor	--tac-border	#e5e7eb

Raw CSS variables — any key beginning with -- is written through verbatim, for the finer details that have no friendly alias (--tac-code-bg, --tac-footer-height, --tac-progress-color, …).

Cover

Key	Values	Default
coverLayout / coverVariant	centered · image-bg · image-title · split · stacked · minimal	centered
sectionVariant	centered · toc · toc-side · number · backdrop · color-block · bigtype	centered
tocHeading	section · deck · none	section

Footer visibility, one key per layout (names are kebab-case and match the slide layout):

footer.title: false        // cover slide
footer.section: false      // section dividers (#)
footer.media: false        // media slides
footer.big-number: false   // big-number slides
footer.quote: true         // quote slides
footer.standard: true      // standard slides
footer.two-column: true    // two-column
footer.three-column: true  // three-column
footer.grid: true          // grid
footer.code-window: true   // code-window
footer.image-and-text: true // image-and-text

Comments are welcome

Inside a .tt file you can write comments with // or #, either on their own line or right after a value (accent: #003087 // brand blue). They're stripped when the theme loads.

How settings stack up

Configuration is applied in cascading layers, from the most general to the most specific. Each layer overrides the one before it:

default.tt (built-in)
    ↓ overridden by
Your .tt theme file
    ↓ overridden by
Deck frontmatter
    ↓ overridden by
Per-slide frontmatter

That's what makes themes flexible. You can use a .tt for the overall design and still tweak a single color in one deck's frontmatter:

===
theme: ./my-theme.tt
accent: #ff6b6b
===