NavigationRailItem_Stylesheet.yaml

One destination in a navigation rail: an icon in a pill, with a label under it.

The look of NavigationRailItem (in Navigation rail). How component stylesheets work.

The stylesheet

# NavigationRailItem: the look of each part of the component, by the part's id.
# A value in {{ }} is one of the component's parameters.
styles:
  - id: root
    style:
      width: 80
      height: 56
      flex_direction: vertical
      align_content: top
      gap: 4
  - id: pill
    style:
      width: 56
      height: 32
      corner_radius: 16
      background:
        if: "{{ selected }}"
        then: secondary_container
        else: transparent
      align_content: center
  - id: icon
    style:
      width: 24
      height: 24
      foreground:
        if: "{{ selected }}"
        then: on_secondary_container
        else: on_surface_variant
  - id: label
    style:
      foreground:
        if: "{{ selected }}"
        then: on_surface
        else: on_surface_variant

How it is tied to the component

NavigationRailItem_Component.yaml holds the structure: the parts, each with an id. This file holds the look: each rule's id names a part, and its style is what that part looks like. When a view uses component: NavigationRailItem, Tesserae fills in the parameters (a value like "{{ width }}" becomes the width the view passed), picks a branch of any if:, and puts each rule under the style the part already has, so a part's own style: always wins.

The parts

root (Container)

Field	Value	What it does
width	80	Pixels, auto (its content's size, or stretched), or a percentage of the parent such as 50%.
height	56	Pixels, auto (its content's size, or stretched), or a percentage of the parent such as 50%.
flex_direction	vertical	How its children are laid out: horizontal (the default) or vertical.
align_content	top	Where its children sit: top_left, top, top_right, left, center, right, bottom_left, bottom or bottom_right. Not set, they fill the space across the layout.
gap	4	Space between its children.

pill (Rect)

Field	Value	What it does
width	56	Pixels, auto (its content's size, or stretched), or a percentage of the parent such as 50%.
height	32	Pixels, auto (its content's size, or stretched), or a percentage of the parent such as 50%.
corner_radius	16	Pixels, or a shape token (none to extra_large, or full for a pill or circle). Per corner: a list [top_left, top_right, bottom_right, bottom_left], or a mapping of corners and edges (top, right, bottom, left) with the rest square.
background	secondary_container if selected, else transparent	Its fill: a theme role such as surface, #RRGGBB, any CSS colour, or a gradient such as linear-gradient(90deg, primary, tertiary).
align_content	center	Where its children sit: top_left, top, top_right, left, center, right, bottom_left, bottom or bottom_right. Not set, they fill the space across the layout.

icon (Icon)

Field	Value	What it does
width	24	Pixels, auto (its content's size, or stretched), or a percentage of the parent such as 50%.
height	24	Pixels, auto (its content's size, or stretched), or a percentage of the parent such as 50%.
foreground	on_secondary_container if selected, else on_surface_variant	Its text or glyph colour: a theme role, #RRGGBB, any CSS colour, or a gradient.

label (Text)

Field	Value	What it does
foreground	on_surface if selected, else on_surface_variant	Its text or glyph colour: a theme role, #RRGGBB, any CSS colour, or a gradient.

What it makes

With label: Go, icon: home, selected: False, each part's style is:

root: {width: 80, height: 56, flex_direction: vertical, align_content: top, gap: 4}
pill: {width: 56, height: 32, corner_radius: 16, background: transparent, align_content: center}
icon: {width: 24, height: 24, foreground: on_surface_variant}
label: {foreground: on_surface_variant}

Changing it

Put a NavigationRailItem_Stylesheet.yaml next to your views. Its rules go over this file's, field by field:

styles:
  - id: pill
    style: {background: tertiary}