@font-face {
  font-family: 'isonorm';
  src: url('../css/fonts/isonorm.eot');
  src: url('../css/fonts/isonorm.eot?#iefix') format('embedded-opentype'),
       url('../css/fonts/isonorm.woff2') format('woff2');
  font-weight: normal;
  font-style: normal;
}

body {
    margin:0 auto;
    background-color: #ffffff;
    text-align: justify;
    font-family: 'isonorm', arial, serif;
    position:relative;
}

#linie_1 {
        background-color:#000000;
        position:absolute;
        margin-top:198px;
        width:100%;
        min-width:1000px;
        height:2px;
        margin-left:0px;
        z-index: 50;
}

#linie_2 {
        background-color:#000000;
        position:absolute;
        margin-top:610px;
        width:100%;
        min-width:1000px;
        height:2px;
        z-index: 50;
}

#zentrierung {
    margin:0 auto;
    min-width:1000px;
    width:1000px;
    left:20%;
    right: -20%;
    background-color: #ffffff;
    background-repeat:repeat-y;
}

#header {
        background-color: none;
        position:relative;
        margin-top:20px;
        height:200px;
        min-width:1000px;
        width:1000px;
        border-style:none;
}

#header-menue_1 {
        background-color: #ffffff;
        position:absolute;
        top:100px;
        left:25px;
        margin:0px;
        height:30px;
        width:449px;
}

#header-dropdown {
        background-color: none;
        position:absolute;
        top:161px;
        left:10px;
        height:40px;
}

<!-- DROPDOWNMENÜ -->

.navbar {
  overflow: hidden;
  background-color: #7a7a7a;
  font-family: 'isonorm', verdana, sans-serif;
}

.navbar a {
  float: left;
  font-size: 18px;
  color: white;
  text-align: center;
  padding: 10px 15px;
  text-decoration: none;
}

.dropdown {
  float: left;
  overflow: hidden;
}

.dropdown .dropbtn {
  cursor: pointer;
  font-size: 18px;
  border: none;
  outline: none;
  color: #000000;
  padding: 10px 15px;
  background-color: #ffffff;
  font-family: 'isonorm', verdana, sans-serif;
  margin: 0;
}

.navbar a:hover, .dropdown:hover .dropbtn, .dropbtn:focus {
  background-color: #e5e5e5;
}

.dropdown-content {
  display: none;
  position: absolute;
  background-color: #ffffff;
  min-width: 160px;
  box-shadow: 0px 0px 20px 0px rgba(0,0,0,0.6);
  z-index: 50;
}

.dropdown-content a {
  float: none;
  color: black;
  padding: 10px 16px;
  text-decoration: none;
  display: block;
  text-align: left;
}

.dropdown-content a:hover {
  background-color: #e5e5e5;
}

.show {
  display: block;
}

<!-- DROPDOWNMENÜ -->

#center {
        background-color:#ffffff;
        position:relative;
        width:980px;
        margin-bottom:0px;
        margin-left:10px;
}

#inhalt_1 {
        position:relative;
        top:0px;
        left:0px;
        width:650px;
        float:left;
        background-color:#ffffff;
        padding:10px;
        z-index:4;
}

#inhalt_home {
        position:relative;
        top:0px;
        left:10px;
        width:650px;
        float:left;
        background-color:#ffffff;
        padding:0px;
        z-index:4;
}

#slideshow {
        margin-left:0px;
        margin-top:0px;
        width:650px;
        height:390px
}

#inhalt_2 {
        position:relative;
        margin-left:670px;
        width:290px;
        height:390px;
        background-color:#ffffff;
        padding:10px;
        z-index:2;
}

#inhalt_2_ohnehoehe {
        position:relative;
        margin-left:670px;
        width:290px;
        background-color:#ffffff;
        padding:10px;
        z-index:2;
}

#bottom {
        background-color:#ffffff;
        position:relative;;
        padding:10px;
        width:960px;
        margin-left:10px;
        margin-top:1px;
}

.imagedropshadow {
    padding: 0px;
    border: solid 1px #ffffff;
}

a:hover img.imagedropshadow {
    border: solid 1px #CCC;
    -moz-box-shadow: 0px 0px 8px #999;
    -webkit-box-shadow: 0px 0px 8px #999;
    box-shadow: 0px 0px 8px #999;
}


        <!--
        A:link {font-weight : normal; color : #000000; text-decoration : none;}
        A:visited {font-weight : normal; color : #000000; text-decoration : none;}
        A:hover {font-weight : normal; color : #7a7a7a; text-decoration : none;}
        B {font-weight : normal; color : #7a7a7a; text-decoration : none;}
        STRONG {font-weight : normal; color : #7a7a7a; text-decoration : none;}
        -->