Customize the embed with CSS variables

You can fully customize the look and feel of the Cal.com embed by passing CSS variables through the Cal("ui", { cssVarsPerTheme }) API. This lets you match the Booker to your brand’s colors, spacing, and border radius — for both light and dark themes.

Pass the variable name without the -- prefix as the key in cssVarsPerTheme. For example, to override --cal-brand, use "cal-brand": "#6F61C0".

Variable reference

Brand

Key	Purpose
`cal-brand`	Primary brand color — selected date circle, confirm button bg
`cal-brand-emphasis`	Brand hover state — confirm button hover
`cal-brand-text`	Text on brand surfaces — “Confirm” button label, selected date number
`cal-brand-subtle`	Lighter brand accent — secondary indicators
`cal-brand-accent`	Contrasting accent on brand buttons — icon color on brand bg

Text

Key	Purpose
`cal-text`	Default body text — event description, time slot labels “14:30”
`cal-text-emphasis`	High-priority text — event title, month header “April 2026”
`cal-text-subtle`	Secondary text — day-of-week headers “SUN MON TUE”, timezone label
`cal-text-muted`	Lowest contrast text — disabled date numbers, placeholder text
`cal-text-inverted`	Text on dark/inverted backgrounds — tooltips

Text semantic

Key	Purpose
`cal-text-semantic-info`	Info alert text — “Scheduling information” notice
`cal-text-semantic-attention`	Warning alert text — “Limited spots left” notice
`cal-text-semantic-error`	Error alert text — “This time is unavailable”

Text status

These feed the text-info / text-error / text-success / text-attention utility classes as well as matching fill-* icon colors within the Booker (for example, Badge variants and form validation messages).

Key	Purpose
`cal-text-info`	Info badge text and icon fill
`cal-text-success`	Success badge text and icon fill
`cal-text-attention`	Attention/warning badge text and icon fill
`cal-text-error`	Error text and icon fill — form validation “Required field”

Background

Key	Purpose
`cal-bg`	Main booker background — the white canvas behind everything
`cal-bg-emphasis`	Highlighted surface — hovered date cell, active date range bg
`cal-bg-subtle`	Secondary surface — time slot hover bg, card backgrounds
`cal-bg-muted`	Faintest surface — unavailable day bg, gradient fade edges
`cal-bg-inverted`	Inverted surface — dark overlay backgrounds, tooltips
`cal-bg-attention`	Warning badge background — “orange” badge variant
`cal-bg-error`	Error badge/alert background — “red” badge variant

Background semantic

Key	Purpose
`cal-bg-semantic-info-subtle`	Subtle info alert background
`cal-bg-semantic-attention-subtle`	Subtle warning alert background
`cal-bg-semantic-error-subtle`	Subtle error alert background

Border

Key	Purpose
`cal-border`	Default dividers — calendar grid lines, card borders
`cal-border-emphasis`	Strong borders — focused input ring, active section border
`cal-border-subtle`	Soft borders — date picker separator, time slot dividers
`cal-border-muted`	Faintest borders — inner column dividers
`cal-border-error`	Error input border — red ring on invalid form field
`cal-border-semantic-error`	Semantic error border — error banner outline
`cal-border-semantic-attention-subtle`	Warning banner border
`cal-border-semantic-error-subtle`	Subtle error banner border

Booker border

Key	Purpose
`cal-border-booker`	Outer border color of the entire booker widget
`cal-border-booker-width`	Thickness of the outer booker border — for example, “1px” or “3px”

Border radius

Key	Purpose
`radius`	Base radius — controls all border-radius sizes across the booker. All sized variants (sm, md, lg, xl) are derived from this value. Set to `0px` for fully sharp corners.

Spacing

Key	Purpose
`spacing`	Base spacing unit — all padding/margin/gap values scale from this

Full example

Cal("ui", {
  theme: "light",
  hideEventTypeDetails: false,
  cssVarsPerTheme: {
    light: {
      // ── Brand ──
      "cal-brand": "#6F61C0",             // Selected date circle, confirm button bg
      "cal-brand-emphasis": "#5A4EA6",     // Confirm button hover state
      "cal-brand-text": "#FFFFFF",         // Text on brand surfaces — "Confirm" label, selected date number
      "cal-brand-subtle": "#B8B0E0",       // Lighter brand accent for secondary indicators
      "cal-brand-accent": "#FFFFFF",       // Contrasting accent on brand buttons

      // ── Text ──
      "cal-text": "#6F61C0",              // Default body text — event description, time slot labels
      "cal-text-emphasis": "#4D408D",      // High-priority text — event title, month header
      "cal-text-subtle": "#8A7FCC",        // Secondary text — day-of-week headers, timezone
      "cal-text-muted": "#C0B8FF",         // Lowest contrast text — disabled dates, placeholders
      "cal-text-inverted": "#FFFFFF",      // Text on dark/inverted backgrounds

      // ── Text Semantic ──
      "cal-text-semantic-info": "#3B3080",        // Info alert text
      "cal-text-semantic-attention": "#8B3A1A",   // Warning alert text
      "cal-text-semantic-error": "#7C2020",       // Error alert text

      // ── Text Status ──
      "cal-text-info": "#3B3080",          // Info badge text and icon fill
      "cal-text-success": "#1A5C30",       // Success badge text and icon fill
      "cal-text-attention": "#8B3A1A",     // Attention badge text and icon fill
      "cal-text-error": "pink",            // Error text and icon fill — form validation

      // ── Background ──
      "cal-bg": "#FFFFFF",                 // Main booker background
      "cal-bg-emphasis": "#E1DFFF",        // Highlighted surface — hovered date, active range
      "cal-bg-subtle": "#F0EEFF",          // Secondary surface — time slot hover, cards
      "cal-bg-muted": "#F8F7FF",           // Faintest surface — unavailable day bg, gradient edges
      "cal-bg-inverted": "#2D2554",        // Inverted surface — dark overlays, tooltips
      "cal-bg-attention": "#FFF3E0",       // Warning badge background
      "cal-bg-error": "#FFE8EC",           // Error badge/alert background

      // ── Background Semantic ──
      "cal-bg-semantic-info-subtle": "#F0EDFF",       // Subtle info alert bg
      "cal-bg-semantic-attention-subtle": "#FFF3E0",  // Subtle warning alert bg
      "cal-bg-semantic-error-subtle": "#FFE8EC",      // Subtle error alert bg

      // ── Border ──
      "cal-border": "#A090E0",                             // Default dividers — calendar grid lines
      "cal-border-emphasis": "#4D408D",                    // Strong borders — focused inputs
      "cal-border-subtle": "#A090E0",                      // Soft borders — separators, dividers
      "cal-border-muted": "#D6D0F0",                       // Faintest borders
      "cal-border-error": "#FFAAAA",                       // Error input border
      "cal-border-semantic-error": "#FFAAAA",              // Error banner outline
      "cal-border-semantic-attention-subtle": "#FFD4A0",   // Warning banner border
      "cal-border-semantic-error-subtle": "#FFAAAA",       // Subtle error banner border

      // ── Booker Border ──
      "cal-border-booker": "#A090E0",      // Outer border of the entire booker widget
      "cal-border-booker-width": "3px",    // Thickness of the outer booker border

      // ── Border Radius ──
      "radius": "0.25rem",                // Base radius — all sizes derive from this (default 10px)

      // ── Spacing ──
      "spacing": "1px",                   // Base spacing unit — all padding/margin/gap scale from this
    },
    dark: {
      // ── Brand ──
      "cal-brand": "#A090E0",
      "cal-brand-emphasis": "#C0B8FF",
      "cal-brand-text": "#1A1540",
      "cal-brand-subtle": "#5A4EA6",
      "cal-brand-accent": "#1A1540",

      // ── Text ──
      "cal-text": "#D6D0F0",
      "cal-text-emphasis": "#F0EEFF",
      "cal-text-subtle": "#A090E0",
      "cal-text-muted": "#8A7FCC",
      "cal-text-inverted": "#1A1540",

      // ── Text Semantic ──
      "cal-text-semantic-info": "#A8A0F0",
      "cal-text-semantic-attention": "#E0A060",
      "cal-text-semantic-error": "#F08080",

      // ── Text Status ──
      "cal-text-info": "#C0B8FF",
      "cal-text-success": "#80E0B0",
      "cal-text-attention": "#F0C090",
      "cal-text-error": "#FFB0B0",

      // ── Background ──
      "cal-bg": "#1A1540",
      "cal-bg-emphasis": "#2D2554",
      "cal-bg-subtle": "#231E4A",
      "cal-bg-muted": "#1E1845",
      "cal-bg-inverted": "#F0EEFF",
      "cal-bg-attention": "#6E2D14",
      "cal-bg-error": "#601818",

      // ── Background Semantic ──
      "cal-bg-semantic-info-subtle": "#1E1860",
      "cal-bg-semantic-attention-subtle": "#3E1E0A",
      "cal-bg-semantic-error-subtle": "#3E1010",

      // ── Border ──
      "cal-border": "#4D408D",
      "cal-border-emphasis": "#8A7FCC",
      "cal-border-subtle": "#3B3080",
      "cal-border-muted": "#231E4A",
      "cal-border-error": "#802020",
      "cal-border-semantic-error": "#802020",
      "cal-border-semantic-attention-subtle": "#6E2D14",
      "cal-border-semantic-error-subtle": "#802020",

      // ── Booker Border ──
      "cal-border-booker": "#4D408D",
      "cal-border-booker-width": "3px",

      // ── Border Radius ──
      "radius": "0.25rem",                // Base radius — all sizes derive from this (default 10px)

      // ── Spacing ──
      "spacing": "1px",
    },
  },
});

Getting Started

Open Source Contribution

Guides

Customize the embed with CSS variables

Variable reference

Brand

Text

Text semantic

Text status

Background

Background semantic

Border

Booker border

Border radius

Spacing

Full example

​Variable reference

​Brand

​Text

​Text semantic

​Text status

​Background

​Background semantic

​Border

​Booker border

​Border radius

​Spacing

​Full example

Variable reference

Brand

Text

Text semantic

Text status

Background

Background semantic

Border

Booker border

Border radius

Spacing

Full example