Layout

How wide your content can stretch on large screens, and how much space is kept at the screen edges. Also sets up the back-to-top button.

Where to find it: In the theme editor, click the gear icon (Theme settings) in the left sidebar, then open Layout.

Good for

Keeping lines of text and product grids at a comfortable width on very wide monitors
Giving the store more breathing room at the screen edges on phones

Width	The widest your content will stretch on large screens. On wider screens, the content stays centered with empty space on both sides. Full-width sections ignore this limit.Adjustable from 960px to 1920px (default 1440px).
Margin	The space kept between your content and the left and right edges of the screen, most noticeable on phones and tablets.Adjustable from 10px to 100px (default 20px).

Show back to top	Adds a small button that scrolls the shopper back to the top of the page after they scroll down.On by default.
Position	Which bottom corner of the screen the back-to-top button sits in.Choose Left or Right (default).

1200–1440px suits most stores. Wider layouts spread product grids thin and make long text lines hard to read.
Full-width sections ignore the page width. Sections with a full-width option stretch edge to edge whatever you set here, so you can mix contained and full-bleed sections.
Keep the margin at least 16px on phones. Text touching the edge of the screen is hard to read and looks cramped.