You can achieve this by adding these CSS rules to your id #left:
position: sticky; // See link
top: 0; //to make it stick to the top of the screen
height: 100vh; // make the height equal to 100 view height
Link for sticky position: Sticky position with nothing but CSS
sticky is a new value for the position property, added as part of CSS3 Layout Module Spec. It acts similarly to relative positioning, in that it doesn’t remove anything from the document flow. In other words, a sticky element has no effect on the position of adjacent elements and doesn’t collapse its parent element.
Hope it helps you
EDIT (fix jumpy behaviour)
In order to avoid the left part to jump up at the end of the page, just add the following CSS rule to your id #left:
box-sizing: border-box;
See updated code snippet:
body {
margin: 0 0 0 0;
}
#container {
display: grid;
grid-template-columns: 50% 50%;
}
.section {
padding: 5% 5% 5% 5%;
}
#left {
background-color: aquamarine;
position: sticky;
top: 0;
height: 100vh;
box-sizing: border-box;
}
#right {
background-color: beige;
}
<div id="container">
<div id="left" class="section">
<p>This should not scroll</p>
</div>
<div id="right" class="section">
<p>
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla aliquet consectetur purus nec volutpat. Donec vel libero nec est commodo facilisis vel et nisl. Praesent porta sed eros eu porta. Cras dolor nulla, ullamcorper et tincidunt quis, porta ut tellus. Maecenas cursus libero sed accumsan luctus. Integer sed consequat ante. Morbi sit amet lectus tempor elit tempor cursus ut sed enim. Donec placerat bibendum volutpat.
</p>
<p>
Nunc sit amet eleifend sapien, sed tincidunt neque. Donec id sapien et nunc scelerisque iaculis dignissim nec mauris. Fusce at pretium nulla. Maecenas vel rutrum tellus, a viverra nunc. Aenean at arcu vitae dui faucibus dapibus. Vivamus hendrerit blandit mollis. Aenean sit amet lectus a metus faucibus condimentum. Proin vel eros ut elit pharetra lacinia vitae eu orci. Etiam massa massa, aliquam at pulvinar ut, porttitor eu mauris. Ut in iaculis sapien.
</p>
<p>
In vitae rhoncus arcu. Maecenas elementum nunc quis magna finibus, vitae imperdiet diam pulvinar. Phasellus sit amet nibh eu massa facilisis luctus. Nulla ullamcorper sodales ante id vestibulum. Fusce felis nisi, lacinia sit amet mauris vel, euismod suscipit neque. Mauris quis libero eget enim facilisis pharetra. Fusce non ligula auctor nunc pretium dignissim eget eget turpis. Nam ultricies dolor ac libero maximus vestibulum. Mauris et tortor vitae nisi ultrices vestibulum ac id mauris. Proin interdum dapibus sollicitudin. Phasellus ultricies vulputate sem id hendrerit. Cras eget posuere nunc, in placerat velit. Pellentesque sed ante at elit ornare efficitur. Donec sed condimentum nisl. Curabitur dapibus leo id ligula dignissim pharetra.
</p>
</div>
</div>