Solo lets you choose the width at which your layout collapses — and, separately, the width at which the menu turns into a hamburger. This video covers both.
Two settings that are easy to confuse
On the Layout & Dimensions tab of Global Site Settings you will find Website's Breakpoints and Menu's Breakpoints. Both offer the same five widths — 576, 768, 992, 1200 and 1400 pixels — and both default to 992. They are independent. A site can keep its columns to 1200px while the menu collapses at 768px, which is often exactly what you want: navigation survives longer than a four-column footer does.
Only what you choose gets loaded
This is the part worth knowing. Solo does not ship one giant responsive stylesheet with every breakpoint in it. Each choice maps to its own library, and only the selected one is attached to the page — five layout files and five menu files exist on disk, and a visitor downloads one of each. Changing the setting swaps the file rather than adding overrides on top of overrides.
The collapse-order checkbox
Between the two selectors sits Tick this box to modify the layout collapse order. It changes how a grouped region reflows into a responsive grid on smaller screens, and its help text is specific: it only applies when the grouped region contains exactly three or four regions. On a two-region group it does nothing, which is not a bug.
Picking a value
Match the breakpoint to your content, not to a device name. A three-column footer usually needs to break earlier than a two-column main area, and a menu with eight top-level items collapses sooner than one with three. Understanding small screen sizes goes into how to choose. Note that Solo also declares a separate set of responsive-image breakpoints at 414, 576, 992, 1200 and 1400 pixels in its breakpoints file; those drive image styles and are not the same control.
Solo runs on ^10.1 || ^11 || ^12 with PHP 8.1 or newer. Download it from the Solo theme page.
If you would rather have this set up for you, Drupal theming services covers the work, and recent projects show the result.
