Styling Decision Tree

Tailwind class exists? → className="..." Dynamic value? → style={{ width: ${x}% }} Conditional styles? → cn("base", condition && "variant") Static only? → className="..." (no cn() needed) Library can't use class?→ style prop with var() constants

Critical Rules

Never Use var() in className

// ❌ NEVER: var() in className <div className="bg-[var(--color-primary)]" /> <div className="text-[var(--text-color)]" />

// ✅ ALWAYS: Use Tailwind semantic classes <div className="bg-primary" /> <div className="text-slate-400" />

Never Use Hex Colors

// ❌ NEVER: Hex colors in className <p className="text-[#ffffff]" /> <div className="bg-[#1e293b]" />

// ✅ ALWAYS: Use Tailwind color classes <p className="text-white" /> <div className="bg-slate-800" />

The cn() Utility

import { clsx } from 'clsx'; import { twMerge } from 'tailwind-merge';

export function cn(...inputs: ClassValue[]) { return twMerge(clsx(inputs)); }

When to Use cn()

// ✅ Conditional classes <div className={cn("base-class", isActive && "active-class")} />

// ✅ Merging with potential conflicts <button className={cn("px-4 py-2", className)} /> // className might override

// ✅ Multiple conditions <div className={cn( "rounded-lg border", variant === "primary" && "bg-blue-500 text-white", variant === "secondary" && "bg-gray-200 text-gray-800", disabled && "opacity-50 cursor-not-allowed" )} />

When NOT to Use cn()

// ❌ Static classes - unnecessary wrapper <div className={cn("flex items-center gap-2")} />

// ✅ Just use className directly <div className="flex items-center gap-2" />

Style Constants for Charts/Libraries

When libraries don't accept className (like Recharts):

// ✅ Constants with var() - ONLY for library props const CHART_COLORS = { primary: "var(--color-primary)", secondary: "var(--color-secondary)", text: "var(--color-text)", gridLine: "var(--color-border)", };

// Usage with Recharts (can't use className) <XAxis tick={{ fill: CHART_COLORS.text }} /> <CartesianGrid stroke={CHART_COLORS.gridLine} />

Dynamic Values

// ✅ style prop for truly dynamic values <div style={{ width: ${percentage}% }} /> <div style={{ opacity: isVisible ? 1 : 0 }} />

// ✅ CSS custom properties for theming <div style={{ "--progress": ${value}% } as React.CSSProperties} />

Common Patterns

Flexbox

<div className="flex items-center justify-between gap-4" /> <div className="flex flex-col gap-2" /> <div className="inline-flex items-center" />

Grid

<div className="grid grid-cols-3 gap-4" /> <div className="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-4 gap-6" />

Spacing

// Padding <div className="p-4" /> // All sides <div className="px-4 py-2" /> // Horizontal, vertical <div className="pt-4 pb-2" /> // Top, bottom

// Margin <div className="m-4" /> <div className="mx-auto" /> // Center horizontally <div className="mt-8 mb-4" />

Typography

<h1 className="text-2xl font-bold text-white" /> <p className="text-sm text-slate-400" /> <span className="text-xs font-medium uppercase tracking-wide" />

Borders & Shadows

<div className="rounded-lg border border-slate-700" /> <div className="rounded-full shadow-lg" /> <div className="ring-2 ring-blue-500 ring-offset-2" />

States

<button className="hover:bg-blue-600 focus:ring-2 active:scale-95" /> <input className="focus:border-blue-500 focus:outline-none" /> <div className="group-hover:opacity-100" />

Responsive

<div className="w-full md:w-1/2 lg:w-1/3" /> <div className="hidden md:block" /> <div className="text-sm md:text-base lg:text-lg" />

Dark Mode

<div className="bg-white dark:bg-slate-900" /> <p className="text-gray-900 dark:text-white" />

Arbitrary Values (Escape Hatch)

// ✅ OK for one-off values not in design system <div className="w-[327px]" /> <div className="top-[117px]" /> <div className="grid-cols-[1fr_2fr_1fr]" />

// ❌ Don't use for colors - use theme instead <div className="bg-[#1e293b]" /> // NO