Embedding
Your site on your own website, in a frame that resizes itself and sets no cookies.
The snippet
It is on the site's own Embed dialog, filled in and ready to copy. The dialog offers two heights.
Auto height is the default. It is two lines: an iframe with no border at the full width of where you put it, and a small script that matches the frame's height to the site as it changes. There is no gap underneath and no scrollbar inside, so it reads as part of your page. Until the site has loaded, the frame keeps the height written in the snippet; if your page builder drops the script, that height stays and the site scrolls inside it rather than being cut off.
Fixed height is one line: a frame of the height you choose, with a scrollbar inside when the site is taller. It needs no script, so it works where scripts can't be pasted.
A site that fills the screen, with a height of 100vh, grows with its frame. Auto height notices, and the frame stays at about the height it started with rather than growing without end.
Which sites may
By default, anywhere. If you list domains, only those may frame it and everywhere else sees a placeholder — enforced by the browser through frame-ancestors, not by us checking a referrer, which anyone can set to anything.
Why it looks like your website
Because it is on your website. The frame has no chrome, no badge on paid plans, and no styling of ours — what renders is what you published. On Free there is a small mark in the corner.
Why it is a frame at all
Every site is served from its own hostname, separate from Solta and separate from every other site. That boundary is what makes it safe for you to put somebody else's code on your own site: it cannot read your cookies, your storage, or your DOM. A script tag that injected the code directly into your website would give all three away.
The frame is only that boundary. With auto height it has no border and no scrollbar of its own, so it sits in your page like the rest of it.