Themes

svblock uses CSS custom properties (variables) for all visual styling of the generated SVG diagrams. Four built-in themes are provided, and custom themes can be defined in TOML or YAML files.

Built-in Themes

Select a theme with the --theme CLI option:

svblock module.sv --theme dark

default: Light background with colored pins. Blue inputs, red outputs. Good for general use and embedding in documentation.
dark: Dark background inspired by Catppuccin. Pastel-colored pins on a dark surface. Suitable for dark-mode documentation or presentations.
minimal: Monochrome – all pins use the same gray color. Clean look for formal documentation where color coding is not needed.
print: Pure black-and-white. Designed for printing and high-contrast display.

CSS Variables

Every theme defines the following 12 CSS custom properties:

Variable	Purpose	Default Value
`--sym-bg`	Diagram background color	`#ffffff`
`--sym-border`	Box border color	`#333333`
`--sym-text`	Module name text color	`#111111`
`--sym-pin-input`	Input pin & label color	`#1a6db5`
`--sym-pin-output`	Output pin & label color	`#b52a1a`
`--sym-pin-inout`	Inout pin & label color	`#6a2ab5`
`--sym-pin-iface`	Interface pin & label color	`#1a9e55`
`--sym-group-bg`	Group separator background	`#f0f0f0`
`--sym-group-text`	Group label text color	`#555555`
`--sym-bus-stroke`	Bus pin stroke width (unitless)	`3`
`--sym-header-bg`	Header/title bar background	`#e8e8e8`
`--sym-param-text`	Parameter text color	`#666666`

Custom Themes

Create a TOML or YAML file that overrides any subset of the CSS variables. Values you don’t specify are inherited from the default theme.

TOML Format

# my_theme.toml
[theme]
"--sym-bg" = "#f5f5dc"
"--sym-border" = "#8b4513"
"--sym-pin-input" = "#006400"
"--sym-pin-output" = "#8b0000"
"--sym-header-bg" = "#deb887"

YAML Format

# my_theme.yaml
theme:
  "--sym-bg": "#f5f5dc"
  "--sym-border": "#8b4513"
  "--sym-pin-input": "#006400"
  "--sym-pin-output": "#8b0000"
  "--sym-header-bg": "#deb887"

Use the custom theme:

svblock module.sv --theme my_theme.toml

Note

Both flat and nested formats are supported. The [theme] / theme: key is optional – you can also put the variables at the top level.

YAML support requires pyyaml. TOML is supported natively on Python 3.11+; on Python 3.10, install tomli.

Theme in Sphinx

The Sphinx directive also accepts themes:

.. svblock:: path/to/module.sv
   :theme: dark