cal-ui-skills

name	cal-ui-skills
description	Cal's UI design system. Use when building interfaces inspired by Cal's aesthetic - light mode, Inter font, 4px grid.
license	MIT
metadata	{"author":"design-skills","version":"1.0.0","source":"https://cal.com"}

Cal UI Skills

Opinionated constraints for building Cal-style interfaces with AI agents.

When to Apply

Reference these guidelines when:

• Building light-mode interfaces
• Creating Cal-inspired design systems
• Implementing UIs with Inter font and 4px grid

Colors

• SHOULD use light backgrounds for primary surfaces
• MUST use #FDFDFD as page background (surface-base)
• SHOULD reduce color palette (currently 16 colors detected)
• MUST maintain text contrast ratio of at least 4.5:1 for accessibility

Semantic Tokens

Token	HEX	RGB	Usage
surface-base	#FDFDFD	rgb(253,253,253)	Page background
surface-raised	#EDEDED	rgb(237,237,237)	Cards, modals, raised surfaces
surface-overlay	#1C1C1C	rgb(28,28,28)	Overlays, tooltips, dropdowns
text-primary	#6B6B6B	rgb(107,107,107)	Headings, body text
text-secondary	#A1A1A1	rgb(161,161,161)	Secondary, muted text
text-tertiary	#404040	rgb(64,64,64)	Additional text
border-default	#E5E5E5	rgb(229,229,229)	Subtle borders, dividers
destructive	#FCC9C1	rgb(252,201,193)	Error states, delete actions

Typography

• MUST use Inter as primary font family
• SHOULD use single font family for consistency
• MUST use 70px / 700 for primary headings
• MUST use 16px / 400 for body text
• SHOULD reduce font weights (currently 5 detected)
• MUST use text-balance for headings and text-pretty for body text
• SHOULD use tabular-nums for numeric data
• NEVER modify letter-spacing unless explicitly requested

Text Styles

Style	Font	Size	Weight	Color	Count
heading-1	Inter	70px	700	#2A2A2A	1
text-23px	Inter	23px	semi_bold	#C1C1C1	1
text-22px	Inter	22px	semi_bold	#494949	1
text-21px	Inter	21px	500	#676767	1
text-21px	Inter	21px	semi_bold	#383838	1
text-19px	Inter	19px	500	#2C2C2C	1
text-19px	Inter	19px	500	#3C3C3C	1
text-19px	Inter	19px	500	#D4D4D4	1
text-18px	Inter	18px	500	#404040	1
body	Inter	16px	400	#A4A4A4	1

Typography Reference

Font Families:

• Inter (used 65x)

Font Sizes: 8px, 9px, 10px, 11px, 12px, 13px, 14px, 15px, 16px, 18px, 19px, 21px, 22px, 23px, 70px

Spacing

• MUST use 4px grid for spacing
• SHOULD use spacing from scale: 1px, 2px, 3px, 4px, 5px, 6px, 7px, 9px
• SHOULD use 5px as default gap between elements
• NEVER use arbitrary spacing values (use design scale)
• SHOULD maintain consistent padding within containers

Borders

• MUST use border-radius from scale: 1px, 2px, 3px, 4px, 6px, 7px, 8px, 9px, 10px, 11px
• SHOULD limit border widths to: 1px, 3px
• SHOULD use 3px as default border-radius
• NEVER use arbitrary border-radius values (use design scale)
• SHOULD use subtle borders (1px) for element separation

Border Radius Reference

Scale: 1px, 2px, 3px, 4px, 6px, 7px, 8px, 9px, 10px, 11px

Layout

• MUST design for 1920px base viewport width
• SHOULD use consistent element widths: 16px, 8px, 11px, 10px, 52px
• SHOULD maintain text-heavy layout with clear hierarchy
• NEVER use h-screen, use h-dvh for full viewport height
• MUST respect safe-area-inset for fixed elements
• SHOULD use size-* for square elements instead of w-* + h-*

Detected Layout Patterns

• Main Content: width: 1565px, height: 814px
• Main Content: width: 1920px, height: 1080px
• Main Content: width: 1180px, height: 717px
• Main Content: width: 1178px, height: 701px

Components

Buttons

Variant	Background	Text	Border	Height	Radius
Ghost	transparent	#6B6B6B	none	-	-

Interactive States

Focus

• MUST use 2px outline with accent color (#5E6AD2)
• MUST use 2px outline-offset
• NEVER remove focus indicators

Hover

• Buttons (primary): lighten background by 10%
• Buttons (secondary): use #EDEDED background
• List items: use #EDEDED background

Disabled

• MUST use opacity: 0.5
• MUST use cursor: not-allowed

Interaction

• MUST use an AlertDialog for destructive or irreversible actions
• SHOULD use structural skeletons for loading states
• MUST show errors next to where the action happens
• NEVER block paste in input or textarea elements
• MUST add an aria-label to icon-only buttons

Animation

• NEVER add animation unless it is explicitly requested
• MUST animate only compositor props (transform, opacity)
• NEVER animate layout properties (width, height, top, left, margin, padding)
• SHOULD use ease-out on entrance animations
• NEVER exceed 200ms for interaction feedback
• SHOULD respect prefers-reduced-motion

Performance

• NEVER animate large blur() or backdrop-filter surfaces
• NEVER apply will-change outside an active animation
• NEVER use useEffect for anything that can be expressed as render logic