{source}
<!-- You can place html anywhere within the source tags -->

<div class="suchdiv_home">

<p id="kott">Find your holiday in one of our self-catering holiday homes</p>

<form name="quickfind" action="contact-us"method="POST">

<div class="holder">

<label for="anreise">Arrival</label>

<input type="date" name="anreise" id="anreise" value="2019-01-12" onchange="anreise_change()" >

</div>

<div class="holder">

<label for="abreise">Departure</label>

<input type="date" name="abreise" id="abreise" value="2019-01-19">

</div>

<div class="holder">

<label for="personenanzahl">Number of guests</label>

<select id="personenanzahl" name="personen">

<option value="8">8</option>

<option value="9">9</option>

<option value="10">10</option>

<option value="11">11</option>

<option value="12" selected="selected">12</option>

<option value="13">13</option>

<option value="14">14</option>

<option value="15">15</option>

<option value="16">16</option>

<option value="17">17</option>

<option value="18">18</option>

<option value="19">19</option>

<option value="20">20</option>

<option value="21">21</option>

<option value="22">22</option>

</select>

</div>
<div class="suchButton">
<button type="button" id="myBtn" onclick="urlaub_bestimmen()">Online booking</button>
<input type="submit" value="Free inquiry">
</form>

</div>
</div>

<!-- The Modal Box -->
<div id="myModal" class="modal">

  <!-- Modal content -->
  <div class="modal-c2">

<span class="close">&times;</span>
   <p id="demo"></p>
  </div>
</div>

<script language="Javascript">
<!-- basiswerte -->
var today = new Date();
var dd = today.getDate();
var mm = today.getMonth()+1; //January is 0! 
var yyyy = today.getFullYear(); 
if(dd<10){
 dd='0'+dd 
} 
if(mm<10){ 
mm='0'+mm 
}

today = yyyy+'-'+mm+'-'+dd; 
document.getElementById("anreise").min = today; 
document.getElementById("anreise").value = today;

var help = new Date();

var today1 = help.getMilliseconds(help);
console.log(today1 );
today1 = today1 + (3 * 24 * 60 * 60 * 1000);
console.log(today1 );
help = new Date();

help.setMilliseconds(today1);

var dd1 = help.getDate();

var mm1 = help.getMonth()+1; //January is 0! 
var yyyy1 = help.getFullYear(); 
if(dd1<10){
 dd1='0'+dd1 
} 
if(mm1<10){ 
mm1='0'+mm1 
}
console.log( dd1+" " + mm1 + " " + yyyy1);
today = yyyy1+'-'+mm1+'-'+dd1; 
console.log(today );
document.getElementById("abreise").min = today; 
document.getElementById("abreise").value = today;


    </script>

<script language="Javascript">

 
 function urlaub_bestimmen()
 {
 var arrival = document.getElementById("anreise").value;
 var departur = document.getElementById("abreise").value;
 var personen = document.forms.quickfind.personen.value;

var a = new Date(arrival);

var d = new Date(departur);

var nights= new Date((d.getTime()-a.getTime())).getDate()-1;

var month = a.getMonth();

var day= a.getDate();

var date = a.getFullYear();

if((month+1) < 10){

date = date + "0";

}

date = date + "" + (month+1);

if(day < 10){

date = date + "0";

}

date = date + "" + day;

 

var link = "https://web4.deskline.net/accoktn/en/accommodation/detail/KTN/cac27306-ea70-4d14-829e-83a6442b0c63/Ferienhäuser_Römerhütte_und_Anderles-Alm?lkcs=H00398&customToolboxHide=true&Dosearch=yes&selNumbersofUnits=1";

 link = link +"&selArrivalDate="+date;

link = link + "&selNights=" +nights;

link = link + "&selAdultsSearchLine1=" +personen;

document.getElementById("demo").innerHTML = '<embed src="'+link+'">';

modal.style.display = "block";

body.classList.add("modal-open");

}

 

// Get the modal
var modal = document.getElementById('myModal');

// Get the button that opens the modal
var btn = document.getElementById("myBtn");

// Get the <span> element that closes the modal
var span = document.getElementsByClassName("close")[0];
var body = document.body;

// When the user clicks on <span> (x), close the modal
span.onclick = function() {
    modal.style.display = "none";
    body.classList.remove("modal-open");
}



</script>

<script language="Javascript">
 function anreise_change()
{
var help = new Date(document.getElementById("anreise").value);


var today1 = help.getTime();
console.log(today1 + " help: "+ help );
today1 = today1 + (3 * 24 * 60 * 60 * 1000);
console.log(today1 + " help: "+ help );
help = new Date(today1);
console.log(today1 + " help: "+ help );


var dd1 = help.getDate();

var mm1 = help.getMonth()+1; //January is 0! 
var yyyy1 = help.getFullYear(); 
if(dd1<10){
 dd1='0'+dd1 
} 
if(mm1<10){ 
mm1='0'+mm1 
}

today1 = yyyy1+'-'+mm1+'-'+dd1; 
document.getElementById("abreise").min = today1; 
document.getElementById("abreise").value = today1;
console.log(today1 + " help: "+ help + " today: " + today1);
}
</script>

{/source}