Terraform giving error for regex Pattern. ValidationException Value 'Regex pattern to check ' at 'description' failed to satisfy constraint

Question

#main.tf

resource "aws_wafv2_ip_set" "ipset" {
  name               = "Tfipset"
  description        = "IP set made from Terraform"
  scope              = "CLOUDFRONT"
  ip_address_version = "IPV4"
  addresses          = ["10.111.0.0/32"]
}

#Creating regex pattern
resource "aws_wafv2_regex_pattern_set" "regex_pattern" {
  name        = "regex-pattern"
  description = "Regex pattern to check "
  scope       = "CLOUDFRONT"

  regular_expression {
    regex_string = var.pattern
  }

  tags = {
    Tag1 = "Test"
  }
}

I am trying to create regex pattern which I will be using later in the script to create AWS Waf. Regex is string should end with .html . So my regex value is "[^"]+\.html" which I am passing like "(?<=\\\")[^\\\"]+\\.html(?=\\\")" . But terraform is failing to interpret it and giving me error :

Error: Error creating WAFv2 RegexPatternSet: ValidationException: 1 validation error detected: Value 'Regex pattern to check ' at 'description' failed to satisfy constraint: Member must satisfy regular expression pattern: ^[\w+=:#@/\-,\.][\w+=:#@/\-,\.\s]+[\w+=:#@/\-,\.]$
        status code: 400, request id: ecd07339-7384-4daa-8044-66a4eb9436e5

#var.tf

variable "pattern" {
  type = string
  default = "(?<=\\\")[^\\\"]+\\.html(?=\\\")"
}

How to do this ?