Issue with content scrolling over banner and under header

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