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Component CSS

Class names & style guide

CSS classes in interkit components should follow this style:

  • There are 2 addressing schemes
    • one for internal use for the component editor
    • one for external use to write optional stylesheets for existing components

internal classes

you are free to use internal classes utilising svelte’s scoped css. Example:

<script>
  // file name: MyComponent.svelte
  export let type = "default"
  export let selected = true
</script>

<div 
  class="container ${type}"
  class:selected
  >
  <span class="item">
  </span>
</div>

<style>
  .container {}
  .container.selected {}
  .container.default {}
  .item {}
</style>

External classes

External classes roughly follow the BEM system

  • the component container should have a class that is the component name, for example MyContainer
  • classes of children should be prefixed with the component name and __, for example MyContainer__MyChild
  • Variations should be prefixed with --

Example:

<script>
  // file name: MyComponent.svelte
  export let type = "default"
  export let selected = true
</script>

<div 
  class="MyComponent MyComponent--${type}"
  class:MyComponent--selected={selected}
  >
  <span class="MyComponent__item">
  </span>
</div>

External stylesheet example:

  #Theming .MyComponent {}
  #Theming .MyComponent--selected {}
  #Theming .MyComponent--default {}
  #Theming .MyComponent__item {}

Combination

You may combine the internal and external style

<script>
  // file name: MyComponent.svelte
  export let type = "default"
  export let selected = true
</script>

<div 
  class="MyComponent MyComponent--${type} container ${type}"
  class:selected
  class:MyComponent--selected={selected}
  >
  <span class="item MyComponent__item">
  </span>
</div>

Spacing & sizing variables

General scale/size, rems

We use rems almost everywhere. This way, the complete app UI can be scaled uniformly using the scale style token. While it is exposed as the --scale CSS variable, the main functionality is provided by hooking it into your apps root <html style="font-size">.

New components should use rems wherever possible to support this functionality.

Notable exceptions where we don’t use rem

  • border-widths of 1px
  • media queries: devices sizes in px
  • min-heights of touch targets in px (like Buttons) to guarantee accessibility
  • ems in certain complex CSS geometrical drawings (e.g. Chat/MessageTyping)

Distances, lengths, margins, paddings

Building on the flexibility of rems, all distances will be scaled accordingly, but can also be influenced by more fine-grained factors:

  1. --distance-scale-factor is the default if nothing else is set. A value of 1.0 should have no effect; 1.1 should increase all distances by 10%, and so on.
  2. --inset will affect all inner distances where direction (horizontal/vertical) doesn’t, shouldn’t, or mustn’t matter.
    (Like a container’s padding which has to play nice with surrounding, or embedded border-radiuses.)
  3. --inset-x and --inset-y will affect inner distances where direction does matter.
    This way, you can affect a Button’s vertical (top/bottom) and horizontal (left/right) separately.
  4. Similarly, --outset-x and --outset-y will affect outer distances where direction does matter.
    (Like the gap between items in a list.)

The code usually follows this pattern:
(more on the values of rems below)

.item {
  /* single values */
  margin-bottom: calc(var(--outset-y) * 1rem);
  padding: calc(var(--inset) * 0.5rem);
}
.button {
  /* two values */
  padding:
    calc(var(--inset-y) * 0.25rem)  /* vertical, top&bottom, note the -y */
    calc(var(--inset-x) * 0.25rem); /* horizontal, left&right, note the -x */
}
.foo-card-header {
  /* all four values */
  padding:
    calc(var(--inset-y) * 0.5rem)   /* top, note the y */
    calc(var(--inset-x) * 1rem)     /* right, note the x */
    calc(var(--inset-y) * 1rem)     /* bottom, y*/
    calc(var(--inset-x) * 2rem);    /* left, x */
}

rem values, visual rhythm

To keep a harmonious visual appearance that is also easily extensible, we limit the distances to simple fractions and multiples of our base unit, the rem.

decimal examples of usage
⅛ 0.125rem tiny distances between
¼ 0.25rem small inner vertical paddings of Buttons
½ 0.5rem most inner paddings (inset), small outer margins (outset-y)
1 1rem most inner paddings of containers with border-radius
1½ 1.5rem some larger paddings of “lofty” containers
2, 3… 2rem, 3rem… large outer margins, small image sizes

We also use odder values like ⅜=0.375rem, or occasionaly sixteenths (0.0625rem, 0.3125rem) if needed.
Typography is an art, not a science ;-)