* {
    box-sizing: border-box;
}

body {
    font-family: Arial;
    padding: 10px;
    background: #f1f1f1;
}

/* header Title */
.header {
    padding: 30px;
    text-align: center;
    background: black;
    color: #00FF00;
}

div.retro_gallery {
    border: 1px solid #ccc;
}

div.retro_gallery:hover {
    border: 1px solid #777;
}

div.retro_gallery img {
    width: 100%;
    height: auto;
}

div.desc {
    padding: 15px;
    text-align: center;
}

/*
* {
    box-sizing: border-box;
}*/

.retro responsive {
    padding: 0 6px;
    float: left;
    width: 24.99999%;
}

.header h1 {
    font-size: 50px;
}

h2 {
    background: black;
    color: #ffffff;
    padding-left: 5px;
    font-weight: bold;
}

#select_menue {
    font-family: Arial;
    font-weight: bold;
    font-size: 20px;
    background-color: #000000;
    color: #ffffff;
    width: 99%;
}

#btn_select_submit {
    margin-top: 10px;
    font-family: Arial;
    font-weight: bold;
    font-size: 20px;
    background-color: #000000;
    color: #ffffff;
}


/* top navigation bar */
.topnav {
    overflow: hidden;
    background-color: #3e3e3e;
}

/* topnav links */
.topnav a {
    float: left;
    display: block;
    color: #00FF00;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
}

/* change color on hover */
.topnav a:hover {
    background-color: #ddd;
    color: black;
}

/* animation in right column */
.retro-anim {
  width: 20px;
  height: 20px;
  background-color: #ffffff;
  position: relative;
  animation-name: retro-animation;
  animation-duration: 4s;
  animation-iteration-count: 30;
}

@keyframes retro-animation {
  0%   {background-color: #ffffff; left:0px; top:0px;}
  50%  {background-color:#cccccc; left:270px; top:0px;}
  75%  {background-color:#00FF00; left:270px; top:0px;}
  100%  {background-color:#ffffff; left:0px; top:0px;}
  
 
}

/* Create two unequal columns that floats next to each other */
/* left column */
.leftcolumn {
    float: left;
    width: 75%;
}

/* right column */
.rightcolumn {
    float: left;
    width: 25%;
    background-color: #f1f1f1;
    padding-left: 20px;
    text-align: center;
}

/* links */
.rightcolumn a {
    color: black;
    padding : 5px;
    background: #f1f1f1;    
}

/* mouse over */
.rightcolumn a:hover {
    background-color: #000000;
    color: #00FF00;
    padding : 5px;
}

/* container for exibit image and description */
.container {
    display: grid;
    column-gap: 50px;
    grid-template-columns: auto auto auto;
    background-color: #ffffff;
    padding: 10px;
    width: auto;
}

.container > div {
    background-color: #f1f1f1;
    border: 1px solid black;
    padding: 20px;
    font-size: 17px;
    width: auto;
}

.container a {
    color: black;
    padding : 5px;
    background: #f1f1f1;
}

/* image */
.museum_image {
    background-color: #f0f0f0;
    width: auto;
    padding: 20px;
    text-align: center;
}

/* image in right column */
.r_col_image {
    background-color: #f1f1f1;
    width: auto;
    text-align: center;
    color: #000000;
}

.r_column_card {
    background-color: white;
    padding: 20px;
    margin-top: 20px;
}

/* image */

.image {
    width: 99%;
    height:300px;
}

/* add a card effect for articles */
.card {
    background-color: white;
    padding: 20px;
    margin-top: 20px;
}

/* clear floats after the columns */
.row::after {
    content: "";
    display: table;
    clear: both;
}

/* footer */
.footer {
    padding: 20px;
    text-align: center;
    background: #000000;
    margin-top: 20px;
    color: #00FF00;
}

/* footer links */
.footer a {
    color: #00FF00;
    text-align: center;
    padding: 5px 5px 5px 5px;
    text-decoration: none;
}

/* change color on hover */
.footer a:hover {
    background-color: #ddd;
    color: black;
}


@media screen and (max-width: 1180px) {
    .leftcolumn, .rightcolumn {
        width: 100%;
        padding: 0;
    }

    .header h1 {
        font-size: 30px;
    }

    /* image */

    .image {
        width: 99%;
        height: auto;
    }

    .retro_responsive {
        /*width: 49.99999%;*/
        margin: 6px 0;
    }

    .container {
        grid-template-columns: 1fr; /* Nur eine Spalte */
    }
}


@media screen and (max-width: 400px) {
    .topnav a {
        float: none;
        width: 100%;
    }

    .header h1 {
        font-size: 25px;
    }

    /* image */

    .image {
        width: 99%;
        height: auto;
    }

    .retro_responsive {
        width: 100%;
    }

    .clearfix:after {
        content: "";
        display: table;
        clear: both;
    }

    .container {
        grid-template-columns: 1fr; /* Nur eine Spalte */
    }
}