can't scroll all the way down because of header - html

Question

i only want my content (without navigation bars and header) scroll-able and not the whole page.
i have been trying for hours playing with positions, overflows and more.
i think it has something to do with the header...
i am frustrated - can anyone help?
thanks in advance!
website: https://jsfiddle.net/ronz2/0zxc13yv/3/
#import url(https://fonts.googleapis.com/css?family=Open+Sans:400,700,800,300);
*
{
margin: 0;
padding: 0;
box-sizing: border-box;
}
html
{
height: 100%;
}
body
{
font-family: 'Open Sans';
height: 100%;
min-height: 100%;
box-sizing: border-box;
overflow: hidden;
}
a
{
text-decoration: none;
}
div#header
{
width: 100%;
height: 62px;
background-color: #2980b9;
margin: 0;
}
div#mssg
{
display: inline-block;
margin: 7px;
padding: 2px;
text-align: center;
border-width: 5px;
border-color: #67C8FF;
border-style: solid;
-webkit-transition: 0.1s;
-moz-transition: 0.1s;
transition: 0.1s;
}
div#mssg p
{
font-size: 1.5em;
color: White;
}
div#mssg:hover
{
margin-top: 5px;
padding-top: 4px;
padding-bottom: 4px;
border-style: solid dashed solid dashed;
}
.logo
{
float: left;
margin-top: 4px;
margin-left: 15px;
}
.logo img
{
width: 140px;
}
div#container
{
margin-top: 62px;
width: 100%;
margin: 0;
height: 100%;
}
.sidebar
{
width: 250px;
height: 100%;
min-height: 100%;
background-color: #171717;
float: left;
}
.topbar
{
width: 100%;
background-color: #171717;
text-align: center;
}
ul#topnav li
{
display: inline-block;
list-style: none;
-webkit-transition: 0.2s;
-moz-transition: 0.2s;
transition: 0.2s;
}
ul#topnav img
{
width: 10px;
-webkit-transition: 0.2s;
-moz-transition: 0.2s;
transition: 0.2s;
}
ul#topnav li a
{
display: inline-block;
color: #ccc;
font-size: 1em;
padding-left: 5px;
padding-right: 5px;
margin-right: 0px;
border-left: 1px solid #67C8FF;
border-right: 1px solid #67C8FF;
-webkit-transition: 0.2s;
-moz-transition: 0.2s;
transition: 0.2s;
}
ul#topnav li a:hover
{
background-color: Gray;
color: #fff;
}
ul#topnav li a:hover img
{
-webkit-transform: rotate(90deg);
-moz-transform: rotate(90deg);
transform: rotate(90deg);
}
ul#topnav ul
{
display: none;
}
ul#topnav li:hover > ul
{
display: block;
background-color: #171717;
position: absolute;
}
ul#topnav ul li
{
display: block;
margin-left: 0px;
}
ul#topnav ul li a
{
display: block;
width: 130px;
border-bottom: 1px solid #67C8FF;
border-top: 1px solid #67C8FF;
}
ul#nav li
{
list-style: none;
border-bottom: 1px solid #67C8FF;
border-top: 1px solid #67C8FF;
}
ul#nav li a
{
color: #ccc;
display: block;
padding: 10px;
font-size: 1em;
-webkit-transition: 0.2s;
-moz-transition: 0.2s;
transition: 0.2s;
}
ul#nav li a:hover
{
background-color: #030303;
color: #fff;
padding-left: 30px;
}
div#content
{
width: auto;
height: 100%;
background-image: url("../Images/spaceBG.jpg");
background-size: cover;
background-repeat: no-repeat;
padding: 15px;
overflow-y: scroll;
}
div#content h1
{
color: White;
text-shadow: 4px 0 9px rgba(86,170,255,0.9) , 0 0 30px rgba(14,134,209,1) , 0 0 30px rgba(14,134,209,1);
}
div#content p
{
color: White;
font-size: 1em;
text-shadow: 2px 1px Black;
}
div#box
{
margin-top: 15px;
}
div#box .box-top
{
color: #fff;
text-shadow: 0px 1px #000;
background-color: #2980b9;
padding: 5px;
padding-left: 15px;
font-weight: 300;
font-size: 1.5em;
}
div#box .box-panel
{
padding: 15px;
background-color: rgba(0, 20, 26, 0.89);
color: White;
font-size: 1.5em;
}
div#box .box-panel img
{
vertical-align: middle;
width: 450px;
}
.link
{
color: #67C8FF;
transition: 0.2s;
-webkit-transition: 0.2s;
-moz-transition: 0.2s;
}
.link:hover
{
color: #67C8FF;
text-shadow: 0px 0px 5px White;
}
div#box .box-panel .icon
{
width: 30px;
}
.form
{
margin-top: 10px;
margin-bottom: 10px;
}
.form fieldset legend
{
background-color: #2980b9;
padding: 0 5px 0 5px;
margin: 5px;
}
.field
{
padding-left: 15px;
color: White;
text-shadow: 2px 1px Black;
}
.input
{
padding: 10px 20px;
margin: 5px 0 5px 0;
border: 1px solid #b7b7b7;
border-radius: 3px;
color: rgba(0,142,198,1);
text-overflow: clip;
background-color: White;
-webkit-box-shadow: 0 0 5px 2px rgba(0,0,0,0.5) inset;
box-shadow: 0 0 5px 2px rgba(0,0,0,0.5) inset;
-webkit-transition: all 200ms;
-moz-transition: all 200m;
transition: all 200ms;
}
.input:focus
{
box-shadow: 0 0 5px 2px #2980b9 inset;
}
.options
{
color: White;
width: 150px;
padding: 5px;
font-size: 16px;
line-height: 1;
border-radius: 3px;
background: url(../Images/arrowDown.png) no-repeat right rgba(0,142,198,0.7);
-webkit-appearance: none;
}
.button
{
cursor: pointer;
padding: 10px 20px;
border: 1px solid #018dc4;
-webkit-border-radius: 3px;
border-radius: 3px;
color: rgba(255,255,255,1);
text-overflow: clip;
background: #0199d9;
text-shadow: 0 0 7px rgba(0,0,0,1);
-webkit-transition: all 200ms cubic-bezier(0.42, 0, 0.58, 1) 10ms;
-moz-transition: all 200ms cubic-bezier(0.42, 0, 0.58, 1) 10ms;
transition: all 200ms cubic-bezier(0.42, 0, 0.58, 1) 10ms;
}
.button:hover
{
-webkit-box-shadow: 0 0 4px 2px rgba(126,193,234,1);
box-shadow: 0 0 4px 2px rgba(126,193,234,1);
-webkit-transition: all 300ms cubic-bezier(0.25, 0.46, 0.45, 0.94);
-moz-transition: all 300ms cubic-bezier(0.25, 0.46, 0.45, 0.94);
transition: all 300ms cubic-bezier(0.25, 0.46, 0.45, 0.94);
}
.button:active
{
-webkit-box-shadow: 0 0 4px 1px rgba(0,0,0,0.5) inset;
box-shadow: 0 0 4px 1px rgba(0,0,0,0.5) inset;
-webkit-transition: all 200ms cubic-bezier(0.42, 0, 0.58, 1) 10ms;
-moz-transition: all 200ms cubic-bezier(0.42, 0, 0.58, 1) 10ms;
transition: all 200ms cubic-bezier(0.42, 0, 0.58, 1) 10ms;
}
table
{
border-collapse: collapse;
}
table#imgs
{
padding-left: 95px;
}
table#imgs tr td
{
padding: 15px;
}
.userTable
{
font-size: 20px;
}
.userTable th , .userTable td
{
padding: 0px 2px 0px 2px;
border-bottom: 1px solid #67C8FF;
text-align: left;
border-left: 1px solid #67C8FF;
}
th.userTable
{
text-align: center;
}
.userNum
{
text-align: center;
margin-top: 10px;
}
.visit
{
color: White;
margin: 15px;
}
<head runat="server">
<title>UniSci</title>
</head>
<body>
<div id="container">
<div id="header">
<div class="logo">
<a href="Default.aspx">
<img src="Images/logo.png" alt="logo" /></a>
</div>
</div>
<div class="topbar">
<ul id="topnav">
<li><a href="darkEn.aspx">Dark Energy
</a>
<ul>
<li>Types</li>
</ul>
</li>
<li><a href="darkMat.aspx">Dark Matter
</a>
<ul>
<li>Types</li>
</ul>
</li>
<li><a href="galaxy.aspx">Galaxies
</a>
<ul>
<li>Creation</li>
<li>Types</li>
</ul>
</li>
<li><a href="gasGiant.aspx">Gas Giants
</a>
<ul>
<li>Types</li>
</ul>
</li>
<li><a href="universe.aspx">The Universe
</a>
<ul>
<li>Creation</li>
<li>Destruction</li>
</ul>
</li>
<li><a href="spacetime.aspx">Spacetime
</a>
<ul>
<li>Relativity</li>
</ul>
</li>
<li><a href="supernova.aspx">Supernova
</a>
<ul>
<li>Effect On Earth</li>
</ul>
</li>
<li><a href="star.aspx">Stars
</a>
<ul>
<li>Life Course</li>
</ul>
</li>
<li><a href="starSys.aspx">Star Systems
</a>
<ul>
<li>Multiple star</li>
<li>Types</li>
</ul>
</li>
<li><a href="universe-dest-info.aspx">Universe Death
</a>
<ul>
<li>Big Bounce</li>
<li>Big Crunch</li>
<li>Big Freeze</li>
<li>Big Rip</li>
</ul>
</li>
<li><a href="gravity.aspx">Gravity
</a>
<ul>
<li>Waves</li>
<li>Relativity</li>
</ul>
</li>
<li><a href="big-bang.aspx">Big Bang
</a>
<ul>
<li>Evidence</li>
<li>Misconceptions</li>
</ul>
</li>
<li><a href="black-hole.aspx">Black Holes
</a>
<ul>
<li>Creation</li>
<li>Destruction</li>
</ul>
</li>
<li><a href="wormhole.aspx">Wormholes
</a>
<ul>
<li>Creation</li>
<li>Shape</li>
</ul>
</li>
<li><a href="extra.aspx">Extras
</a>
<ul>
<li>Comets</li>
<li>Asteroids</li>
</ul>
</li>
</ul>
</div>
<div class="sidebar">
<ul id="nav">
<li>Main Page</li>
<li>Login</li>
<li>Register</li>
</ul>
</div>
<div id="content"> <h1>
Galaxy
</h1>
<div id="box">
<div class="box-top">
What types of galaxies are there?
</div>
<div class="box-panel">
Ellipticals:<br />
The Hubble classification system rates elliptical galaxies on <br />
the basis of their ellipticity, ranging from E0, being nearly <br />
spherical, up to E7, which is highly elongated. These galaxies <br />
have an ellipsoidal profile, giving them an elliptical appearance <br />
regardless of the viewing angle. Their appearance shows little structure <br />
and they typically have relatively little interstellar matter. <br />
Consequently, these galaxies also have a low portion of open <br />
clusters and a reduced rate of new star formation. Instead they <br />
are dominated by generally older, more evolved stars that are orbiting <br />
the common center of gravity in random directions. The stars <br />
contain low abundances of heavy elements because star formation ceases <br />
after the initial burst. In this sense they have some similarity to the <br />
much smaller globular clusters.<br />
<br />
Shell galaxy:<br />
A shell galaxy is a type of elliptical galaxy where the stars in <br />
the galaxy's halo are arranged in concentric shells. About one-tenth <br />
of elliptical galaxies have a shell-like structure, which has never<br />
been observed in spiral galaxies. The shell-like structures are <br />
thought to develop when a larger galaxy absorbs a smaller companion<br />
galaxy. As the two galaxy centers approach, the centers start to oscillate <br />
around a center point, the oscillation creates gravitational <br />
ripples forming the shells of stars, similar to ripples spreading on water. <br />
For example, galaxy NGC 3923 has over twenty shells.<br />
<br />
Spirals:<br />
Spiral galaxies resemble spiraling pinwheels. Though the stars and other<br />
visible material contained in such a galaxy lie mostly on a plane, the <br />
majority of mass in spiral galaxies exists in a roughly spherical halo of <br />
dark matter that extends beyond the visible component, as demonstrated <br />
by the universal rotation curve concept. Spiral galaxies consist of a rotating <br />
disk of stars and interstellar medium, along with a central bulge of generally <br />
older stars. Extending outward from the bulge are relatively bright arms. <br />
It appears the reason that some spiral galaxies are fat and bulging while some <br />
are flat discs is because of how fast they rotate.
</div>

Answer 1

The header is not problem,
The body is set to overflow:hidden which is why the bottom will not show

Answer 2

Change the height of the container similar to this:
#container {
margin-top: 62px;
width: 100%;
margin: 0;
height: calc(100% - 131px);
}
The problem is the exact px value you subtract: Depending on the width of the viewport, your nav is spread over a different number of lines. Either fix the height of #topnav or use media queries with different height calculations for #container.
ADDED fiddle: https://jsfiddle.net/s3qeu8vu/