CSS Doesn't Throw: One Mistyped Comment Closer Silently Ate 15 Lines of My Stylesheet

Originally published on hexisteme notes . Every test passed. The page was in pieces. I was rebuilding a small internal dashboard — FastAPI, Jinja2 templates, hand-written CSS, no build step — and the layout had come apart. Timeline rows unstacked into a vertical column. Status dots floated free of their rows. Log group labels overlapped. It looked exactly like a page whose stylesheet had failed to load. The stylesheet had loaded. All 481 tests in the suite were green. And when I grepped the CSS file for the rules that were obviously not being applied, they were sitting right there on disk, correctly written. The cause was a comment closer. Somewhere in the middle of the file, a /* had been closed with #} — Jinja's comment terminator — instead of */ . Muscle memory, from switching back and forth between .html templates and .css . CSS then did precisely what the specification tells it to do: it kept reading. The comment ran on and swallowed the next 15 lines of rules — the timeline-row grid, the feed, the bucket layout, the dot alignment — until it hit the next real */ , seventeen lines down. No error. No console warning. No failing test. The rules were present in the file and absent from the page at the same time. The typo is the least interesting part. What's worth keeping is why CSS is designed to fail without symptoms, why source-level review cannot see it, and why the fix is a two-line assertion rather than more care. Why nothing complained: CSS has no fatal errors The CSS Syntax specification defines comment consumption like this: on seeing /* , consume everything "up to and including the first */ , or up to an EOF code point." No notion of a comment being too long, no heuristic about blank lines or braces, no upper bound. First */ wins. A comment closed seventeen lines later than intended is not a malformed comment — it is a well-formed comment that happens to be seventeen lines long. The parser has no way to know you meant something else. Even if the comment h