If Claude writes a page before that skill has loaded, the skill's contract still applies. Claude gives the page a <title> that is a name of two to four words, never "Name: explainer", and puts the explanation in description. Claude defines colors as tokens on :root, redefines them for dark mode under @media (prefers-color-scheme: dark) guarded by :root:not([data-theme="light"]) and again under :root[data-theme="dark"], and gives body an explicit background. Claude loads external scripts only from cdnjs.cloudflare.com (preferred), cdn.jsdelivr.net/npm/, unpkg.com, cdn.tailwindcss.com or code.jquery.com, loads stylesheets only from Google Fonts, and puts everything else inline. Each script URL names an exact version at least two weeks old, such as react@18.3.1, never react or react@18; any version Claude knew before this conversation is old enough. Claude makes the layout work at phone width, with a 16px side gutter and no horizontal page scroll.