One File Per Design, Built From the Catalog and Your Own Choices
Every design in the catalog carries its own stylesheet, and what reaches a visitor is not the file a theme author wrote. It is assembled: the design's own rules, then the choices you made in your account layered over them, served as one file.
What goes into it
Three things, in order. The design's base rules, which decide the layout, the spacing and the typography. Then the variable parts, which is where your color scheme and grayscale mode live. Then anything you have written yourself under custom CSS, last, so it wins.
Assembling it rather than shipping a static file is what lets two actors on the same design look genuinely different. It is also why a color change appears the moment you save it, instead of waiting on a rebuild.
Why a reference to a missing file costs you something
A stylesheet does not only describe colors and spacing. It also names files: background textures, icon sprites, the font files a typeface needs. Every one of those names is a request the browser makes on top of the page itself.
If a named file is not there, the browser still asks. The request goes out, travels, and comes back with nothing. The visitor sees no error, because there was nothing to draw in the first place, but they waited for the round trip. On a phone on a weak connection, a handful of those is the difference between a page that feels immediate and one that does not.
So the catalog's stylesheets are checked for names with nothing behind them, and those names are removed rather than left in place. The rule that makes it safe to do at scale is narrow: a property whose entire job is the image loses the whole declaration, and a shorthand property loses only the image name, so background colors, positions and repeat keywords survive untouched.
Fonts work the same way, and fail more quietly
A typeface is declared in the stylesheet and its files are fetched separately. When a font file is missing, nothing breaks visibly. The browser falls back to a system typeface and the page renders perfectly well, just not in the face the design intended.
That is the most durable kind of problem there is, because it looks like a design choice. So every font a design declares is fetched and confirmed to be a real font before it is registered, and the families whose symbols the markup actually uses are given a working source rather than being left to fall back.
The related piece on how font loading keeps your layout still covers the other half of this, which is what happens between the fallback and the real face arriving.
Where the rest of the weight goes
Stylesheets are one part of what a page weighs. The bigger levers are covered in lighter stylesheets, web fonts from a CDN, design images on a delivery network and smaller images at the same quality.
None of it is anything you configure. Browse the catalog or create a free actor website.
