html, body  {
    background-image: url("img/building-plan-354233_1920.jpg");
    width: 80%;
    position: relative;
    margin: 0 auto;
    padding: 0;
    /* background-color: hsl(0, 0%, 42%); */
    color:hsl(0, 0%, 100%);
    font-family: Arial, Helvetica, sans-serif;
}
header{
    height: 6em;
        /*                      left img                                right img */
        background-image: url("img/Text_zugeschnitten.png"),url("img/Logo_1000_1000.png");
        background-repeat: no-repeat, no-repeat;
        background-position-x: left, right;
        background-size: 40% auto, 8% auto;
}
nav{
    margin: 0   auto;
    background-color: hsl(198, 54%, 50%, 1);
    position: sticky;
    top: 0;
}
nav ul li{
    list-style-type: none;
    display: inline-block;
    border-right: 1px solid;
    padding: 0em 0.5em;
    margin: 1em 0em;
    position: relative;
}
nav ul li a{
    font-family: Arial, Helvetica, sans-serif;
    color:hsl(0, 0%, 100%);
    font-size: 1.5em;
    display: block;
}
nav ul li a:hover{
    background-color: hsl(0, 0%, 42%, 0.9);
}
nav ul li ul{
    display: none;
    position: absolute;
    background-color: hsl(198, 54%, 50%, 1);
    border-radius: 0px 0px 12px 12px;
}
nav ul li:hover ul{
    display: block;
}
nav ul li ul a{
    float: left;
    color:hsl(0, 0%, 100%);
}
nav ul li ul li{
    float: left;
    margin: 0.5em;
    padding: 0em;
    border-right: none;
    /* position: absolute; */
}
nav ul li ul li a:hover{
    background-color: hsl(0, 0%, 42%, 0.9);
}
nav li:last-child{
    border-right: none;
}

article{
    margin: 0   auto;
    padding: 0.5em 2em;
    font-size: 1.5em;
    /* height: 100em; */
    border: 2px solid hsl(198, 54%, 50%, 1);
    background-color: hsl(0, 0%, 42%, 0.9);
}
footer{
    margin: 1em   auto;
    background-color: hsl(198, 54%, 50%, 1);
    position: sticky;
    bottom: 0;
}
footer li{
    list-style-type:none;
    display:inline-block;
    border-right: 1px solid;
    padding: 0em 0.5em;
    margin: 0.2em 0em;
}
footer li:last-child{
    border-right: none;
}
footer li a{
    color:hsl(0, 0%, 100%);
    font-size: .8em;
}
#zertifikat {
    width: 50%;
    height: 50%;
    display: flex;
    justify-content: center;
    align-items: center;
}
#planpruefung {
    width: 50%;
    height: 50%;
    display: flex;
    justify-content: center;
    align-items: center;
}#home {
    width: 50%;
    height: 50%;
    display: flex;
    justify-content: center;
    align-items: center;    
}
#youtube {
    width: auto;
    height: 1.1em;
}