Code ayuda con error en html

Saludos, alguien me puede ayudar a el error que me da en el html, sobre lo que entiendo soy nuevo hice unos cambios busco encender 2 led con botones de on y off.

#include <ESP8266WiFi.h>
#include <WiFiClient.h> 
#include <ESP8266WebServer.h>

const char *ssid = "WIFI 1";
const char *password = "12345678";
int stateLED = LOW;

ESP8266WebServer server(80);

void handleRoot() {
    response();
}

void A() {
  stateLED = LOW;
  digitalWrite(LED_BUILTIN, stateLED);
  response();
}

void B() {
  stateLED = HIGH;
  digitalWrite(LED_BUILTIN, stateLED);
  response();
}

void C() {
  stateLED = LOW;
  digitalWrite(LED_BUILTIN, stateLED);
  response();
}

void D() {
  stateLED = HIGH;
  digitalWrite(LED_BUILTIN, stateLED);
  response();
}

const String HtmlHtml = "<html><head>"
    "<meta name=\"viewport\" content=\"width=device-width, initial-scale=1\" /></head>";
const String HtmlHtmlClose = "</html>";
const String HtmlTitle = "<h1>Arduino-er: ESP8266 AP WebServer exercise</h1>
\n";
const String HtmlLedStateLow = "<big>LED is now <b>ON</b></big>
\n";
const String HtmlLedStateHigh = "<big>LED is now <b>OFF</b></big>
\n";
const String HtmlButtons = 
    "<a href=\"1\"><button style=\"display: block; width: 100%;\">ON 1</button></a>
"
    "<a href=\"2\"><button style=\"display: block; width: 100%;\">OFF 1</button></a>
";
    "<a href=\"3\"><button style=\"display: block; width: 100%;\">ON 2</button></a>
"
    "<a href=\"4\"><button style=\"display: block; width: 100%;\">OFF 2</button></a>
";

void response(){
  String htmlRes = HtmlHtml + HtmlTitle;
  if(stateLED == LOW){
    htmlRes += HtmlLedStateLow;
  }else{
    htmlRes += HtmlLedStateHigh;
  }

  htmlRes += HtmlButtons;
  htmlRes += HtmlHtmlClose;

  server.send(200, "text/html", htmlRes);
}

void setup() {
    delay(1000);
    Serial.begin(9600);
    Serial.println();

    WiFi.softAP(ssid, password);

    IPAddress apip = WiFi.softAPIP();
    Serial.print("visit: \n");
    Serial.println(apip);
    server.on("/", handleRoot);
    server.on("/1", A);
    server.on("/2", B);
    server.on("/3", C);
    server.on("/4", D);
    server.begin();
    Serial.println("HTTP server beginned");
    pinMode(LED_BUILTIN, OUTPUT);
    digitalWrite(LED_BUILTIN, stateLED);
}

void loop() {
    server.handleClient();
}

Y cual es el error?

me marca error

 "<a href=\"3\"><button style=\"display: block; width: 100%;\">ON 2</button></a>
"

Hay varios errores en esa línea, debería ser asi

const String HtmlButtons = 
    "<a href=\"1\"><button style=\"display: block; width: 100%;\">ON 1</button></a>
"
    "<a href=\"2\"><button style=\"display: block; width: 100%;\">OFF 1</button></a>
"
    "<a href=\"3\"><button style=\"display: block; width: 100%;\">ON 2</button></a>
"
    "<a href=\"4\"><button style=\"display: block; width: 100%;\">OFF 2</button></a>
";