<style>
div.container {
    width: 100%;
    border: 1px solid gray;
}

header, footer {
    padding: 1em;
    color: white;
    background-color: black;
    clear: left;
    text-align: center;
}

nav {
    float: left;
    max-width: 160px;
    margin: 0;
    padding: 1em;
}

.theme_chooser {
    background-color: #343434;
    border: none;
    color: white;
	float: right;
	margin: -1;
}

.mainmenu, .submenu {
  list-style: none;
  padding: 0;
  margin: 0;
}
.mainmenu a {
  display: block;
  background-color: #CCC;
  text-decoration: none;
  padding: 10px;
  color: #000;
}
.mainmenu a:hover {
    background-color: #C5C5C5;
}
.mainmenu li:hover .submenu {
  display: block;
  max-height: 200px;
}
.submenu a {
  background-color: #999;
}
.submenu a:hover {
  background-color: #666;
}
.submenu {
  overflow: hidden;
  max-height: 0;
  -webkit-transition: all 0.5s ease-out;
}

article  {
    margin-left: 170px;
    padding: 1em;
    overflow: hidden;
}

problemhead {
	font-style: oblique;
}
problembody {
	text-align: justify;
	font-style: normal;
}

table {
	margin-left: auto;
	margin-right: auto;
}
table, th, td {
    border: 1px solid black;
}
th, td {
    padding: 5px;
    text-align: center;
}
</style>
