body {
	background : url(bricks.gif);
	font-family: Eras Bold ITC, Arial, Helvetica, sans-serif;
}

h1{ display: block ; text-align : center ; color: blue  ; font-family : Eras Bold ITC, arial ; font-size : 30px }
h2{ display: block ; text-align : center ; color: black ; font-family : arial ; font-size : 25px }
h3{ display: block ; text-align : center ; color: black ; font-family : arial ; font-size : 20px }
h4{ display: block ; text-align : left   ; color: blue  ; font-family : arial ; font-size : 30px }
h5{ display: block ; text-align : left   ; color: black ; font-family : arial ; font-size : 25px }
h6{ display: block ; text-align : left   ; color: black ; font-family : arial ; font-size : 20px }

.video-container {
            display: flex;
            justify-content: center;
            align-items: center;
        }

        video {
            width: 190%;
            max-width: 300px;
        }

.topnav {
  overflow: hidden;
  background-color: #333;
}

.topnav a {
  float: left;
  display: block;
  color: #f2f2f2;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
  font-size: 17px;
}

.topnav a:hover {
  background-color: green;
  color: black;
}

.topnav a.active {
  background-color: blue;
  color: white;
}

.topnav .icon {
  display: none;
}

img.a {
	border: 1px solid black;
	width: auto;
    max-height: 200px;
	margin-left: auto;
	margin-right: auto;
}
 
.center {
	display: block;
    margin: 0 auto;
	text-align: center;
}

.caption {
	text-align:center;
}

	@media screen and (min-width: 500px) {
		p {
			font-size: 16px;
			color: black;
		}
	}
	@media screen and (min-width: 600px) {
		p {
			font-size: 20px;
			color: black;
		}
	}
	@media screen and (min-width: 700px) {
		p {
			font-size: 25px;
			color: black;
		}
	}
	
	
@media screen and (min-width: 1001px) {
	.center20 {
	  margin-left: auto;
	  margin-right: auto;
	  width: 10%;
	}
}

@media screen and (min-width: 1000px) {
	.center20 {
	  margin-left: auto;
	  margin-right: auto;
	  width: 100%;
	}
}	
	
	
table, th, td {
	border: 1px solid black;
		margin-left: auto;
		margin-right: auto;
	}
}


p.ex1 {display: none;}
p.ex2 {display: inline;}
p.ex3 {display: block;}
p.ex4 {display: inline-block;}

.center {
	display: block;
	margin-left: auto;
	margin-right: auto;
	width: 50%;
}

tr:nth-child(even) {
  background-color: #dddddd;
}