Position fixed with 100% height - html

Question

I want use 100% height for MAIN id but when I put it 100% height to main id, creativity class is placed on the main. when use pixel for main in different device its look different.
is there any solution to fix it ?
#main {
width: 100%;
height: 675px;
}
.main {
position: fixed;
width: 100%;
height: 100%;
background: url(/images/logo/logo.svg) center no-repeat #ffcc00;
}
.introduction {
position: relative;
display: inline-block;
z-index: 2;
width: 100%;
height: auto;
background: #fcd803;
text-align: center;
padding-bottom: 40px;
}
.introduction h1 {
text-align: center;
text-transform: uppercase;
font-size: 24px;
padding-top: 40px;
}
.introduction span img {
width: 200px;
padding-top: 30px;
}
.introduction div {
text-align: center;
margin-left: 30px;
margin-right: 30px;
margin-top: 30px;
font-size: 15px;
line-height: 21px;
}
.creativity {
position: relative;
z-index: 2;
width: 100%;
height: 320px;
background: #fcd803;
}
.creativity-img {
display: block;
background: url('/images/ariadesk.png');
background-repeat:no-repeat;
background-size:contain;
background-position:bottom;
width: 100%;
height: 320px;
position: absolute;
}
.creativity-img div {
position: relative;
text-align: center;
padding-top: 145px;
}
.creativity-img div h1 {
font-size: 20px;
font-weight: normal;
text-transform: capitalize;
color: white;
border: solid 2px #fff;
display: inline-block;
padding: 10px 50px;
}
<div id="main">
<div class="main">
<div class="logo"><h1>HUR</h1><br><span>studio</span></div>
<div class="nav">
<ul>
<li>introduction</li>
<li>work</li>
<li>service</li>
<li>client</li>
<li>team</li>
<li>contact</li>
</ul>
</div>
</div>
</div>
<div class="introduction" id="introduction">
<h1>introduction</h1>
<span>
<img src="/images/icon/intro.svg" alt="">
</span>
<div><p>
We are small team of super nerds and talented creatives. Create cutting-edge interfaces and visually stunnig media.<br>
Experts in providing innovative Web Design, Graphic Design, Digital Imaging, Advertising and Branding service</p>
</div>
</div>
<div class="creativity">
<div class="creativity-img"></div>
</div>

Answer 1

If you don't mind IE 8 and below, you can use vh (viewport-height) units:
#main {
width: 100%;
height: 100vh;
}
Fiddle

Answer 2

I think it is because of your position
your #main is in the same level with .creativity
if you want the .main always on the top, just change your .creativity with z-index: 1 AND your .main with z-index: 2
You never set the .main index, and it always on the bottom layer.
Is it that case you want to?