Sticky element not responding. Issue that has not been documented yet apparently - css

Question

No matter what I try, I can't get an image on my test web page get sticky on scroll. It's here: https://www.varamedia.be/website-laten-maken/restaurants/. I want the image of the laptop with the people in it to be sticky on scroll through the other content.
It's a Wordpress site and I also noticed something peculiar, namely the CSS that is not recognizing the sticky css, apparently. The error message is: "expected (static | relative | absolute | fixed) but found 'sticky'." Here is an image of it: https://www.varamedia.be/wp-content/uploads/2019/01/sticky.png
I really appreciate any kind of feedback on this. Thanks a lot for sharing your thoughts.
I read all articles I could get my hands on, tried all proposed solutions from the docs I could find online, but it does not work well for me. The image refuses to become sticky.
I tried using ID's, classes, played around with the overflow:hidden; etc But somehow I am missing something here. Though it feels as if I'm overlooking some detail because the position:sticky; CSS feature looks kind of straightforward but apparently isn't :/
.stickyimage{
position:sticky;
}
I'd welcome any advice based on an inspection of the given URL. Thanks a thousand times for your valuable input.

Answer 1

a 'top' or 'bottom' value must be added.
body {
margin:0;
}
p {
font-size:36px;
line-height:50px;
}
.nav {
width:100%;
background:orangered;
height:60px;
font-size:24px;
color:#fff;
text-align:center;
line-height:60px;
/*following codes is for sticky */
position:sticky;
top:0; /* it's up to you */
}
<p>Lorem ipsum, dolor sit amet consectetur adipisicing elit. Voluptates voluptatum cum optio a natus iste repellendus eaque at aut, voluptatibus sit veritatis quis quam magnam aspernatur, vero, sunt modi magni.</p>
<div class="nav">This a sticky nav</div>
<p>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Magni, delectus! Beatae similique atque voluptas ipsam impedit blanditiis qui reprehenderit, nisi quas odio dolor? Quam rem magnam, deleniti quia itaque iusto.</p>
<p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Omnis modi, debitis minima eveniet et illo laudantium, distinctio mollitia quaerat blanditiis quas. Quo doloribus illum neque. Unde labore ut perspiciatis nobis!</p><p>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Magni, delectus! Beatae similique atque voluptas ipsam impedit blanditiis qui reprehenderit, nisi quas odio dolor? Quam rem magnam, deleniti quia itaque iusto.</p>
<p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Omnis modi, debitis minima eveniet et illo laudantium, distinctio mollitia quaerat blanditiis quas. Quo doloribus illum neque. Unde labore ut perspiciatis nobis!</p><p>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Magni, delectus! Beatae similique atque voluptas ipsam impedit blanditiis qui reprehenderit, nisi quas odio dolor? Quam rem magnam, deleniti quia itaque iusto.</p>
<p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Omnis modi, debitis minima eveniet et illo laudantium, distinctio mollitia quaerat blanditiis quas. Quo doloribus illum neque. Unde labore ut perspiciatis nobis!</p><p>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Magni, delectus! Beatae similique atque voluptas ipsam impedit blanditiis qui reprehenderit, nisi quas odio dolor? Quam rem magnam, deleniti quia itaque iusto.</p>
<p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Omnis modi, debitis minima eveniet et illo laudantium, distinctio mollitia quaerat blanditiis quas. Quo doloribus illum neque. Unde labore ut perspiciatis nobis!</p>

Answer 2

You have 2 issues.
Issue #1 - You must delcare either top, bottom, left or right on the element with position: sticky.
Issue #2 - Your parent element can not have overflow: hidden. Right now both the body tag and the html tag have the following...
overflow-x: hidden;
overflow-y: hidden;
Remove these...
You also need to make sure that the stickyclass is on the correct div, you want it on the outer div, in your example it should be on the following div.
I tested this and it works as expected.