With CSS, you could use the hover event to detect a certain scroll position (e.g. on something just after the red div), but this would not work on touch only devices like mobile phones. It also wouldn't be reliable, as the cursor could be anywhere on the screen.
Using JavaScript to detect scroll position would be necessary. However, you could use the JavaScript only to add a class at different scroll positions and then do the rest with CSS. Here's a simple example:
var red = document.querySelector('#inner-box');
var begin = red.scrollTop;
var end = begin + red.clientHeight;
console.log(begin)
document.body.classList.add('in');
window.addEventListener("scroll", (event) => {
if(this.scrollY < begin) {
document.body.classList.add('before');
document.body.classList.remove('after');
document.body.classList.remove('in');
} else if(end < this.scrollY) {
document.body.classList.remove('before');
document.body.classList.add('after');
document.body.classList.remove('in');
} else {
document.body.classList.remove('before');
document.body.classList.remove('after');
document.body.classList.add('in');
};
});
.headervideo {
background-color: blue;
width: 100%;
height: 900px;
}
.headerbreak {
width: 100%;
height: 300px;
}
.headervideo #inner-box {
background-color: red;
height: 90%;
width: 100%;
}
body {
}
body.before {
background-color: lightgreen;
}
body.in {
background-color: lightpink;
}
body.after {
background-color: lightblue;
}
<body>
<div class="headervideo">
<div id="inner-box"></div>
</div>
<div class="headerbreak">
<div>
</body>