On the Kalles demo, you see the layout of Size Guide page:
Or on the Product page, like this:
If you wanna achieve it for your store, kindly follow the instruction below.
1. Create the Size Guide page
From Shopify Admin > Online Store > Pages > Add page > To create the Size Guide page. Kindly follow my video below:
About the custom HTML code of the Size Guide page, please copy here:
2. Enable Size Chart, Delivery, Ask block
The last step, please go to Customize > Product Page > Default Product > Product Summary > Add block > Add the Size Chart, Delivery, Ask block to Product Summary:
Then, in the HTML Size Chart option > Click the Select page button > Choose the page that you just created.
The page has been selected, as the image below:
After Save change, please preview your store to see the result. It will look like the video below: