Where does user agent stylesheet come from?

basically, i have a html element i want to hide until i make a post request. to hide the element i used display:none; , but this is somehow being overiden by the user agent stylesheet.

enter image description here

ive searched by whole html for the word "block" but it doesnt show up anywhere. i also have no external css everything is inline.

Im hosting this page with djangos devserver...

where is "display: block;" coming from? how do i stop it?

below is a minimal reproducable example if what im doing. im trying to make my div element start hidden until a post request is made.

<form action="http://localhost:8080" method="post" id = "mi_form">
  <input type="submit" name="get prices" value="get prices" />
</form>

<div id = "loader" style = "style= display:none; background:#000000; width:200px; height:200px; ">

</div>

<script type="text/javascript">

  $("#mi_form").submit(function (e) {
              e.preventDefault(); // stops the default action
              $("#loader").show(); // shows the loading screen
              $.ajax({
                  url: test.php,
                  type: "POST"
                  success: function (returnhtml) {
                      $("#loader").hide(); // hides loading sccreen in success call back
                  }
              });
          });

</script>
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