message: feat: add as optional
diff: export interface IButton {
  /** 'default' | 'primary' | 'secondary' */
  - color: 'default' | 'primary' | 'secondary'
  + color?: 'default' | 'primary' | 'secondary'
  /** 'fill' | 'outline' | 'text' */
  - variant: 'filled' | 'outlined' | 'text'
  + variant?: 'filled' | 'outlined' | 'text'
  /** true | 'false */
  disabled?: boolean
  /** href <a> */
  