message: feat: add cssVar assertion
diff: @@ -56,6 +56,10 @@ export function isString(value: any): value is string {
  return Object.prototype.toString.call(value) === "[object String]"
  }
  +export function isCssVar(value: string) {
  + return /^var\(--.+\)$/.test(value)
  +}
  +
  // Event assertions
  export function isInputEvent(value: any): value is ChangeEvent {
  return value && isObject(value) && isObject(value.target)
  