Mobile view of the contact page bug

Question

just such a problem – my contact page has a view bug when in the mobile view – the footer is aroused almost all over the screen and the contact form is on itsee screenshot, I marked the div that obviously causes problems . Checked all the HTML tags – they're OK, tried position of the objects in the CSS – nothing helps. In the desktop view everything looks OKsee screenshot. Here is the HTML document and a CSS file linked there. They are better to copy to an editor to run in a browser.

a {
  color: #f91111;
}

a:hover {
  color: #fff;
  background: #f91111;
  text-decoration: none;
}

body {
  margin: 0;
  padding: 0;
  font-size: 97%;
  line-height: 1.4em;
  min-width: 500px;
  font-family: Helvetica;
  letter-spacing: 101%;
  min-height: 100%;
}

header {
  margin-bottom: 1%;
  background-image: url(../images/DSC00075.JPG);
  background-position: 0% 7%;
  background-size: 100%;
  background-opacity: 0.9;
  background-color: #f91111;
  padding: 1% 0 0%;
  position: fixed;
  z-index: 10;
  width: 100%;
}

.header {
  max-width: 1310px;
  margin: 0 auto;
}

.collapse {
  display: none;
}

.panel-group .panel-heading+.panel-collapse>.panel-body,
.panel-group .panel-heading+.panel-collapse>.list-group {
  border-top: 1px solid #ddd;
}

main {
  margin: 0 auto;
  /* padding: 10% 15% 2.9%; */
  font-size: 94%;
  max-width: 1310px;
  padding-top: 200px !important;
  min-height: calc(74.75vh);
}

nav {
  max-width: 750px;
  text-align: left;
  padding-bottom: 0.85em;
  padding-left: 0.35em;
}

nav a {
  display: inline;
  text-align: left;
  text-decoration: none;
  padding: 2%;
  margin-right: 4.8%;
  border-radius: 5px;
  color: #fff;
  line-height: 1em;
}

nav a:hover {
  background-color: #fff;
  color: #000;
}

a.active {
  background-color: #fff;
  color: #000;
}

.footer {
  font-size: 0.75rem;
  padding: 1.5% 15% 1.25% 14.4%;
  color: #fff;
}

h1 {
  font-size: 4rem;
  padding-bottom: 1rem;
  padding-left: 0.8%;
  color: #fff;
}

h2 {
  font-size: 2.5em;
  color: #f91111;
  margin-bottom: 2.5rem;
  line-height: 1.25em;
}

h3 {
  font-size: 1.3em;
  color: #f91111;
  padding: 0.25% 0%;
}

h3.lebenslauf {
  background: #f91111;
  color: #fff;
  padding: 0.25% 0% 0.25% 1%;
}

.hr4 .lightborder {
  display: block;
  width: 93%;
  border-bottom: 1px solid #e8e8e8;
  position: relative;
  z-index: 1;
}

span.ul-second-line {
  /*padding-left: 10px;*/
  margin-left: 7px;
}

ul.Lebenslauf {
  padding-left: 16px;
  margin-top: 0px;
}

p.no-margin-before {
  -webkit-margin-before: 0;
}

div.button {
  display: inline;
  font-size: 0.75rem;
  padding: 5px;
  margin-right: 10px;
  min-width: 15%;
}

div.table-row {
  max-width: 100%;
  display: block;
  margin-bottom: 0.75rem;
  padding-left: 1px;
  font-size: 0.95em;
}

div.left {
  float: left;
  width: 20%;
  min-width: 150px;
  display: inline;
}

div.right {
  width: 75%;
  display: inline-block;
}

.empty-bottom {
  height: auto;
}

a.up-there {
  text-decoration: none;
  padding: 3px 5px;
}

div.kategorie a.up-there {
  margin-right: -9px;
}

div.kategorie a.up-there:hover {
  margin-right: 0px;
}

.collapse {
  display: none;
}

strong.red-accentuation {
  color: #f91111;
}

footer {
  max-width: 100%;
  background-color: #f91111;
  padding: 0 2%;
  vertical-align: bottom;
}

footer a {
  color: white;
  text-decoration: none;
  margin-bottom: 0;
}

footer a:hover {
  text-decoration: underline;
}

#image {
  text-align: center;
  width: auto;
  border: none;
  margin: 0 auto;
  margin-bottom: 10px;
  background-color: none;
  font-size: 100%;
  background-image: url('');
}

.empty-space {
  text-align: right;
}

#image-alternative {
  text-align: center;
  margin: 0 auto;
  margin-bottom: 10px;
}

.preview {
  width: 10%;
  margin-left: 10px;
  border: 3px solid #f91111;
  border-radius: 5px;
  height: 15%;
}

.container {
  max-width: 95%;
  margin: 3% auto;
  margin-left: 0;
  padding: 10px;
  padding-left: 0;
  background-color: none;
  overflow: hidden;
  box-shadow: none;
}

.gallery ul {
  list-style: none;
  padding: 0;
  margin: 0 auto;
}

.gallery li {
  display: inline;
  width: 50%;
  height: 30vh;
  margin: 2%;
  margin-left: 0;
  position: relative;
  font-size: 0;
}

.modal-open .modal {
  overflow-x: hidden;
  overflow-y: auto;
}

.modal {
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  z-index: 1050;
  display: none;
  overflow: hidden;
  -webkit-overflow-scrolling: touch;
  outline: 0;
}

.fade.in {
  opacity: 1;
}

.fade {
  opacity: 0;
  -webkit-transition: opacity .15s linear;
  -o-transition: opacity .15s linear;
  transition: opacity .15s linear;
}

.referenz-link {
  border: solid 1px #f91111;
  border-radius: 10px;
  width: 200px;
  height: 200px;
  margin-right: 30px;
  margin-bottom: 30px;
  overflow: hidden;
  display: inline-block;
  background: #f91111;
}

.referenz-link:last-child {
  margin-right: 0px;
}

.referenz-link:hover {
  background: none;
}

.picture-keeper {
  overflow: hidden;
  height: 133px;
  margin-bottom: 10px;
  border-bottom: solid 1px #f91111;
  background: #fff;
}

img.reference {
  width: 100%;
}

.notation {
  padding: 0px 10px 15px;
  text-align: center;
}

.referenz-link a {
  color: #fff;
  text-decoration: none;
  font-weight: 700;
}

.referenz-link a:hover {
  color: #f91111;
  background: #fff;
}

h1.header {
  display: inline-block;
}

img.presentation {
  display: block;
  margin-left: -1em;
}

h2.with-picture {
  display: inline-block;
}

.foto-presentation {
  text-align: center;
  margin-bottom: 2.5em;
}

.adress-left {
  display: inline-block;
  float: left;
  width: 48%;
  margin-right: 2%;
}

.form-right {
  display: inline-block;
  width: 48%;
  float: right;
}

dd,
dt {
  display: inline-block;
}

dd {
  margin-left: 0;
}

dt {
  width: 7em;
}

dl {
  -webkit-margin-before: 0;
  -webkit-margin-after: 0;
  -webkit-margin-start: 0px;
  -webkit-margin-end: 0px;
}

address {
  font-style: normal;
}

label.kontaktangabe {
  width: 8em;
  display: inline-block;
}

textarea,
input[type="text"] {
  border: solid 1px #f91111;
  border-radius: 3px;
  padding: 4px;
  line-height: 1.5em !important;
}

textarea {
  font: 400 0.95em Arial;
}

div#nachricht label {
  vertical-align: top;
}

button.buttons {
  color: #fff;
  background: #f91111;
  border: none;
  border-radius: 3px;
  font-size: 14px;
  padding: 7px;
}

button.buttons:hover {
  background: #a60c0c;
}

#kontaktdaten div.table-row {
  font-size: 1em;
}

#kontaktdaten form {
  padding-top: 1em;
}

@media screen and (min-width: 500px) and (max-width: 790px) {
  header {
    background-position: 0% 10%;
    background-size: 100%;
    padding: 1% 1% 1%;
    margin: 0;
  }
  h1 {
    font-size: 3rem;
  }
  nav a {
    padding: 1.5%;
    margin-right: 1%;
    border-radius: 2px;
  }
  nav {
    align: left;
    padding-bottom: 0.1rem;
  }
  main {
    margin: 0% 1%;
    padding: 1%;
  }
  div.left {
    margin-right: 1rem;
    min-width: none;
  }
  .referenz-link {
    width: 200px;
    height: 200px;
    margin-right: 45px;
    margin-bottom: 45px;
  }
  .referenz-link:last-child {
    margin-right: 0px;
  }
  .picture-keeper {
    height: 133px;
  }
  .notation {
    font-size: 1em;
  }
  .adress-left {
    display: block;
    width: 95%;
    margin-bottom: 2em;
  }
  .form-right {
    display: block;
    width: 95%;
    float: left;
  }
  label.kontaktangabe {
    display: block;
  }
}

@media screen and (max-width: 480px) {
  body {
    max-width: 450px;
    font-size: 0.9rem;
    padding: 0%;
  }
  header {
    padding: 0% 1% 1%;
    margin: 0;
    background-position: 0% 0%;
    background-repeat: no-repeat;
    background-size: cover;
  }
  h1 {
    font-size: 2rem;
  }
  nav {
    max-width: 480px;
    align: left;
    padding-bottom: 0.6em;
  }
  nav a {
    display: block;
    text-align: left;
    text-decoration: none;
    padding: 1.5%;
    margin: 0.5% 0%;
    border-radius: 2px;
    max-width: 30%;
  }
  main {
    margin: 0% 0% 0% 1;
    padding: 1% 0% 1% 1%;
    max-width: 450px;
    font-size: 100%;
  }
  div.left {
    width: 100%;
    float: none;
    display: block;
    min-width: 0;
  }
  div.right {
    max-width: 100%;
    display: block;
  }
  .hr4 .lightborder {
    display: block;
    max-width: 100%;
  }
  div.button {
    display: block;
    max-width: 50%;
    text-align: center;
    margin: 0 auto;
  }
  footer {
    max-width: 480px !important;
  }
  .container {
    padding: 0%;
  }
  img.preview {
    margin-left: 0%;
    margin-right: 2%;
  }
  .footer {
    padding: 1.5% 0%;
    max-width: 450px;
  }
  .referenz-link {
    margin-right: 45px;
    margin-bottom: 45px;
  }
  .notation {
    font-size: 1.25em;
  }
  .adress-left {
    display: block;
    width: 95%;
    margin-bottom: 2em;
  }
  .form-right {
    display: block;
    width: 95%;
    float: left;
  }
  label.kontaktangabe {
    display: block;
  }
  textarea.contact-form {
    width: 379px;
  }
  dd,
  dt {
    display: block;
  }
  dd {
    margin-bottom: 1em;
  }
  span.left {
    font-weight: 700;
  }
  .kategorie .table-row {
    margin-bottom: 2rem;
  }
  div#werdegang .table-row {
    margin-bottom: 1em;
  }
}

<!DOCTYPE html>
<html lang="de">

<head>
  <meta charset="UTF-8">
  <title>Peter Schachnowskij – Homepage</title>
  <link rel="stylesheet" href="css/portfolio.css">
</head>

<body>
  <header>
    <div class="header">
      <h1>Peter&nbsp;Schachnowskij</h1>

      <nav>
        <a href="index.html">Startseite</a>
        <a href="Lebenslauf.html">Lebenslauf</a>
        <a href="referenzen.html">Referenzen</a>
        <a href="zeugnisse.html">Zeugnisse</a>
        <a class="active">Kontakt</a>
      </nav>
    </div>
  </header>
  <main>
    <p>&nbsp;</p>
    <h2>Kontakt</h2>
    <div class="table-row" id="kontaktdaten">
      <div class="adress-left">
        <h3>Peter Schachnowskij</h3>
        <p><address>Richterstraße 9<br>
70567 Stuttgart</address></p>
        <p>
          <dl><dt>Tel.:</dt>
            <dd><a href="tel:+49-176-21751711">01 76 / 21 75 17 11</a></dd>
          </dl>
          <dt>E-Mail: </dt>
          <dd><a href="mailto:peter.schachnowskij.gf@gmail.com">peter.schachnowskij.gf@gmail.com</a></dd>
          <p>
            <p>
              <dl><dt>Homepage:</dt>
                <dd><a href="index.html">noch im Aufbau</a></dd>
              </dl>
              <dl><dt>XING-Profil:</dt>
                <dd><a href="https://www.xing.com/profile/Peter_Schachnowskij" target="_blank">https://www.xing.com/profile/Peter_Schachnowskij</a></dd>
              </dl>
            </p>
      </div>
      <div class="form-right">
        <h3>Haben Sie ein Anliegen?</h3>
        <p>Schreiben Sie mir gerne!</p>
        <form action="mailto:peter.schachnowskij.gf@gmail.com" method="post">
          <div class="table-row"><label class="kontaktangabe" for="name">Ihr Name*: </label><input type="text" value size="50" aria-required="true" aria-invalid="false" /></div>
          <div class="table-row"><label class="kontaktangabe" for="vorname">Ihr Vorname*: </label><input type="text" value size="50" aria-required="true" aria-invalid="false" /></div>
          <div class="table-row"><label class="kontaktangabe" for="e-mail">Ihre E-Mail*: </label><input type="text" value size="50" aria-required="true" aria-invalid="false" /></div>
          <div class="table-row"><label class="kontaktangabe" for="telefon">Ihr Telefon: </label><input type="text" value size="50" aria-required="false" aria-invalid="false" /></div>
          <div class="table-row" id="nachricht"><label class="kontaktangabe" for="nachricht">Ihre Nachricht: </label><textarea name="your-message" cols="52" rows="12" class="contact-form" aria-invalid="false"></textarea></div>
          <div class="table-row"><label class="kontaktangabe" for="absenden">&nbsp;</label><button class="buttons" type="submit" name="action" id="absenden">Absenden</button></div>
        </form>
        <div class="empty-bottom">&nbsp;</div>
      </div>
    </div>
  </main>
  <div class="empty-bottom">&nbsp;</div>


  <footer>
    <div class="footer">
      <div class="button">Peter Schachnowskij </div>
      <div class="button">Richterstr. 9 </div>
      <div class="button">70567 Stuttgart </div>
      <div class="button">
        <nobr>Tel.: 01 76 / 21 75 17 11</nobr>
      </div>
      <div class="button">
        <nobr>E-Mail:&nbsp;<a href="mailto:peter.schachnowskij.gf@gmail.com">peter.schachnowskij.gf@gmail.com</a></nobr>
      </div>
    </div>
  </footer>
</body>

</html>

Can someone please help me? Thanx in previous.