html {
    height: 100%;
}
body {
    height: 100%;
    margin: 0;
    background-color: slategray;
    font-family: Arial, Helvetica, sans-serif;
    display: grid;
    justify-items: center; /* left-right center*/
    align-items: center; /* top-bottom center*/
}

a {
    color: darkcyan;
}

#main-holder {
    width: 70%;
    height: 100%;
    justify-items: center; /* left-right center*/
    align-items: center; /* top-bottom center*/
    background-color: white;
    border: black;
    border-radius: 7px;
}

#ui-header {
    text-align: center;
}

.sidebar {
    margin: 5;
    padding: 0;
    width: 150px;
    background-color: lightsteelblue;
    position: fixed;
    height: 50%;
    overflow: auto;
    border-style: inset;
    border-width: 2px;
    border-color: black;
    border-radius: 3px;
}

.sidebar a {
    display: block;
    padding: 10px;
}

.sidebar a.active {
    background-color: antiquewhite;
    color: aqua;
}

.sidebar a:hover:not(.active) {
    background-color: #555;
    color: white;
}

div.content {
    margin-left: 150px;
    padding-left: 15px;
}

/* on mobile make it a top bar */
@media screen and (max-width: 700px) {
    .sidebar {
        width: 100%;
        height: auto;
        position: relative;
    }
    .sidebar a {float: left;}
    div.content {margin-left: 0;}
}

.column {
    float: left;
    width: 25%;
    padding: 10px;
}

.column img {
    opacity: 0.8;
    width: 100%;
    cursor: pointer;
}

.column img:hover {
    opacity: 1;
}

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

.container {
    position: relative;
    display: none;
}

#imgtext {
    position: absolute;
    bottom: 15px;
    left: 15px;
    color: white;
    font-size: 35px;
}

.closebtn {
    position: absolute;
    top: 15px;
    right: 15px;
    color: white;
    font-size: 35px;
    cursor: pointer;
}