JSFiddle - React, Tailwind, and code Playground

HTML

<section>A website!</section>
<div class="uparrow">Up!</div>
<div class="bottomarrow">Down!</div>

CSS

.uparrow, .bottomarrow {
    display: none;
    position: absolute;
    width: 4em;
    height: 4em;
    line-height: 4em;
    text-align: center;
    background-color: #000;
    color: #fff;
    border-radius: 50%;
    cursor: pointer;
}

JavaScript

// Define how wide the areas should be
// where the arrow appears
var top_nav_height = 70;
var bottom_nav_height = 70;

// Get some dimensions
var page_height = $(document).height();
var half_arrow_size = $('.uparrow').width() / 2;

// Listen to the user moving their mouse
$(document).mousemove(function(event) {
    // Where is the mouse?
    var pos_y = event.pageY;    // Distance from top of the page
    var pos_x = event.pageX;    // Distance from left of the page
    var in_area;
    // Leave a 5px space to hide the arrows when 
    // the pointer moves outside of the page
    if (pos_y <= top_nav_height
        && pos_y > 5) {
        in_area = 'top_nav';
    }
    else if (page_height - pos_y <= bottom_nav_height
             && page_height - pos_y > 5) {
        in_area = 'bottom_nav';
    }
    
    // Show the arrow when in a nav area
    switch(in_area) {
            
        // We are in the top nav area
        case 'top_nav': 
            // Show the .uparrow and have it follow the mouse
            $('.uparrow')
                .show()
                .css({
                    top: pos_y - half_arrow_size, 
                    left: pos_x - half_arrow_size
                });
            break;
            
        // We are in the bottom nav area
        case 'bottom_nav':
            // Show the .bottomarrow and have it follow the mouse
            $('.bottomarrow')
                .show()
                .css({
                    top: pos_y - half_arrow_size, 
                    left: pos_x - half_arrow_size
                });
            break;
        
        // We aren't in a nav area
        default:
            // Hide both arrows
            $('.uparrow, .bottomarrow').hide();
    }
    
    // Decide where the arrow should link

});