styling

name	styling
description	CSS and Tailwind, cn(), flex layouts. Use for "style this", "fix the CSS", "add classes", "not scrolling", "overflow", Tailwind utilities.
metadata	{"author":"epicenter","version":"1.0"}

Styling Guidelines

When styling depends on shadcn-svelte structure, class merging, variants, Bits UI composition, or local wrapper behavior, read ui-design's component-system reference for upstream grounding. Ordinary Tailwind utilities and the repo-local layout rules below need no external lookup.

Minimize Wrapper Elements

Avoid creating unnecessary wrapper divs. If classes can be applied directly to an existing semantic element with the same outcome, prefer that approach.

Good (Direct Application)

<main class="flex-1 mx-auto max-w-7xl">
	{@render children()}
</main>

Avoid (Unnecessary Wrapper)

<main class="flex-1">
	<div class="mx-auto max-w-7xl">
		{@render children()}
	</div>
</main>

This principle applies to all elements where the styling doesn't conflict with the element's semantic purpose or create layout issues.

Tailwind Best Practices

• Use the cn() utility from $lib/utils for combining classes conditionally
• Prefer utility classes over custom CSS for local layout and state
• Prefer shared scale and semantic-token utilities over arbitrary bracketed values and raw colors
• Use tailwind-variants for component variant systems
• Follow the background/foreground convention for colors
• Leverage CSS variables for theme consistency

Shared Primitive Overrides

When styling a local @epicenter/ui primitive, use ui-design's component-system reference. Tailwind classes on shared primitives should usually express parent layout or product state, not redefine the primitive's visual budget.

Good primitive overrides:

<Item.Button size="sm" class="w-full justify-start text-left" />

Suspicious primitive overrides:

<Item.Button size="sm" class="gap-2 rounded px-2 py-1.5 text-sm hover:bg-accent/50" />

If an override repeats size, density, radius, gap, padding, typography, hover, focus, or transition classes, ask whether the primitive needs a size, variant, or semantic wrapper instead.

Disabled States: Use HTML disabled + Tailwind Variants

When an interactive element can be non-interactive (empty section, loading state, no items), use the HTML disabled attribute instead of JS conditional guards. Pair it with Tailwind's enabled: and group-disabled: variants.

Why disabled Over JS Guards

• disabled natively blocks clicks: no if (!hasItems) return needed
• Enables the :disabled CSS pseudo-class for styling
• Semantically correct for accessibility (screen readers announce "dimmed" or "unavailable")
• Tailwind's enabled: and group-disabled: variants compose cleanly

Pattern

<!-- The button disables itself when count is 0 -->
<button
  class="group enabled:cursor-pointer enabled:hover:opacity-80"
  disabled={item.count === 0}
  onclick={toggle}
>
  {item.label} ({item.count})
  <ChevronIcon class="group-disabled:invisible" />
</button>

Key Variants

• enabled:cursor-pointer: pointer cursor only when clickable
• enabled:hover:bg-accent/50: hover effects only when interactive
• group-disabled:invisible: hide child elements (e.g., expand chevron) when parent is disabled
• disabled:opacity-50: dim the element when disabled

Anti-Pattern

<!-- Don't do this: JS guard duplicates what disabled does natively -->
<button
  class="cursor-pointer hover:opacity-80"
  onclick={() => { if (item.count > 0) toggle(); }}
>

The JS guard leaves cursor-pointer and hover:opacity-80 active on a non-interactive element. The user sees a clickable button that does nothing. Use disabled and let the browser + CSS handle it.

Flex Column Scroll Trap

When a flex child uses h-full (height: 100%) but shares a flex column with siblings (headers, toolbars, footers), it computes to the full parent height: overflowing past siblings instead of taking the remaining space. The content gets clipped or pushes the layout past the viewport, and scroll areas inside never activate.

This is the single most common layout bug in this codebase. It appears whenever you have:

• A component inside a Resizable.Pane (paneforge) that needs to scroll
• A ScrollArea.Root (bits-ui) or overflow-auto div inside a flex column with a header/toolbar sibling
• Any split-pane or panel layout where one section should scroll independently

The Fix: flex-1 min-h-0 overflow-hidden

Replace h-full with these three utilities on the flex child that contains scrollable content. Each solves a distinct problem:

Utility	What it does	Why it's needed
flex-1	Take remaining space after siblings	h-full = 100% of parent, ignoring siblings. flex-1 = remaining space.
min-h-0	Allow shrinking below content size	Flex items default to min-height: auto, preventing them from being smaller than their content.
overflow-hidden	Establish a bounded height context	Without this, children with overflow-auto or ScrollArea have no height ceiling to scroll against.

All three are required. Missing any one breaks the fix:

• Without flex-1: element is still 100% of parent, overflows siblings
• Without min-h-0: element refuses to shrink, content pushes it taller
• Without overflow-hidden: inner scroll containers have no bounded ancestor, so they expand instead of scrolling

Before / After

<!-- BROKEN: h-full = 100% of parent, ignores the toolbar sibling -->
<main class="flex h-full flex-col overflow-hidden">
  <div class="border-b px-4 py-2">Toolbar</div>
  <MyScrollableContent class="h-full" />  <!-- overflows past main -->
</main>

<!-- FIXED: flex-1 takes remaining space, overflow-hidden bounds it -->
<main class="flex h-full flex-col overflow-hidden">
  <div class="border-b px-4 py-2">Toolbar</div>
  <MyScrollableContent class="flex-1 min-h-0 overflow-hidden" />
</main>

Inside Resizable Panes (paneforge)

Paneforge Pane components set width via flex ratios but do not constrain height or clip overflow. Any scrollable content inside a Pane needs the full flex-1 min-h-0 overflow-hidden chain on its root element:

<Resizable.Pane defaultSize={80}>
  <!-- Pane provides no height constraint or overflow clipping -->
  <div class="flex flex-1 min-h-0 flex-col overflow-hidden">
    <div class="border-b">Header</div>
    <div class="flex-1 overflow-y-auto">
      <!-- this content now scrolls -->
    </div>
  </div>
</Resizable.Pane>

With ScrollArea (bits-ui)

ScrollArea.Root renders with position: relative and its viewport uses height: 100%. This breaks the flex sizing chain: the viewport's percentage height resolves against the relative parent, which has no explicit height in a flex context. The content expands instead of scrolling.

Two options:

1. Prefer plain overflow-y-auto on a div with flex-1 min-h-0 (simpler, always works)
2. If you need styled scrollbars, wrap ScrollArea.Root in a div with flex-1 min-h-0 overflow-hidden to give it a bounded ancestor

<!-- Option 1: Plain overflow (preferred) -->
<div class="flex-1 overflow-y-auto">
  {#each items as item}
    <div>{item.name}</div>
  {/each}
</div>

<!-- Option 2: ScrollArea with bounded wrapper -->
<div class="flex-1 min-h-0 overflow-hidden">
  <ScrollArea.Root class="h-full">
    {#each items as item}
      <div>{item.name}</div>
    {/each}
  </ScrollArea.Root>
</div>

Rule of Thumb

If you write h-full on a flex child that has siblings in the same flex column, stop and replace it with flex-1 min-h-0 overflow-hidden. The h-full pattern only works when the element is the sole child of its flex parent.