Issue with content scrolling over banner and under header - html

Question

So I have this fixed header which has z-index:10, below that a fixed banner and then below that a relative content container. What I want is that the content scrolls over the banner but under the header. However, when I try to scroll it doesn't work. The strange part to me is that whenever I add box-shadow: 0px 0px 2px rgb(100,100,125); to the content container it does do what I want. I'm using the following code:
* {
padding: 0;
margin: 0 auto;
}
body {
background: rgb(223,227,238);
text-align: center;
}
#body_container {
padding-top: 80px;
}
#banner_container {
position: fixed;
left: 0;
right: 0;
}
#banner {
width: 1024px;
height: 300px;
}
#content_container {
background: rgb(243,247,248);
max-width: 1024px;
height: 100%;
position: relative;
top: 300px;
box-shadow: 0px 0px 2px rgb(100,100,125);
}
header {
min-width: 100%;
background: rgb(50,50,50);
height: 80px;
position: fixed;
z-index: 10;
}
/* Header styling, not relevant */
#header_container {
max-width: 1024px;
height: 100%;
}
#header_container div {
float: left;
display: inline-block;
width: 25%;
}
#logo {
width: 50%;
height: auto;
}
.menuItem {
padding-top: 29px;
height: calc(100% - 29px);
border: 0;
text-align: center;
font-family: Signika;
font-size: 25px;
color: rgb(203,207,218);
}
.menuItem:hover {
border-bottom: 4px solid rgb(59,89,202);
height: calc(100% - 33px);
color: rgb(160,170,218);
}
.menuLogo {
padding-top: 14.5px;
height: calc(100% - 14.5px);
border: 0;
text-align: center;
}
#mobile_menu_button {
display: none;
}
<header>
<div id="header_container">
<div class="menuLogo">
<img id="logo" src="img/desygn%20logo%20website.png">
</div>
<div class="menuItem">Home</div>
<div class="menuItem">Over</div>
<div class="menuItem">Contact</div>
<div id="mobile_menu_button">
</div>
</div>
</header>
<div id="body_container">
<div id="banner_container">
<img id="banner" src="img/banner_website.png">
</div>
<div id="content_container">
</div>
</div>

Answer 1

In your code you've not added any content under content_container. I don't see any issue with your code. It is working fine. Check here with content