Colour Functions

Hand-picking hex codes for every shade is tedious and fragile. Sassy lets you derive colours from existing ones using functions powered by Culori.

Derived Colours

Add these to your vars.std group:

vars:
  std:
    fg: $$white
    fg.inactive: fade($(std.fg), 60)
    bg: "#1a1a2e"
    bg.panel: lighten($(std.bg), 15)
    bg.accent: darken($(accent), 70)
    outline: fade($(accent), 30)
    shadow: fade($(std.bg), 80)

Instead of guessing what “60% opacity white” looks like as a hex code, you write fade($(std.fg), 60) and Sassy computes it.

Core Functions

Here are the functions you’ll use most:

Function	What it does	Example
lighten(colour, amount)	Increases lightness by amount%	lighten($(bg), 15)
darken(colour, amount)	Decreases lightness by amount%	darken($(accent), 70)
fade(colour, amount)	Sets opacity to amount%	fade($(fg), 60)
mix(colour1, colour2, weight)	Blends two colours	mix($(accent), $(bg), 50)

The first argument is always a colour — a hex value, a variable reference, or even another function call. The remaining arguments are numeric parameters.

Wire Them Into Your Theme

Add more properties using the derived colours:

theme:
  colors:
    editor.background: $(std.bg)
    editor.foreground: $(std.fg)
    editorGroupHeader.tabsBackground: $(std.bg.panel)
    tab.activeBackground: $(std.bg)
    tab.activeForeground: $(std.fg)
    tab.inactiveBackground: $(std.bg.panel)
    tab.inactiveForeground: $(std.fg.inactive)
    focusBorder: $(std.outline)
    panel.border: $(std.outline)
    editorOverviewRuler.border: $(std.outline)
    widget.shadow: $(std.shadow)
    titleBar.activeBackground: $(std.bg.accent)
    titleBar.activeForeground: $(std.fg)
    titleBar.inactiveBackground: $(std.bg.accent)
    titleBar.inactiveForeground: $(std.fg.inactive)

Build It

npx @gesslar/sassy build ocean.yaml

Open the output and look at the resolved values. fade($(std.fg), 60) becomes something like #e6e6e699 — the same white at 60% opacity, computed automatically. Change your base bg colour and every derived shade updates with it.

Next, let’s add syntax highlighting.