css-to-class

css-to-class

Convert a multi-class HTML element or plain class string into a single, semantically named CSS class. Resolves each utility token to its actual property/value declarations by grepping all .css files in the user's project — works with plain CSS, SCSS output, Tailwind, or any other utility-first workflow.

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Input forms

Form	Example
HTML element	<div class="testimonial flex-grid py-8 items-center" data-flex-grid>
Plain class list	testimonial flex-grid py-8 items-center
Quoted string	"flex py-4 items-center justify-between"

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Name rules

• Max 20 characters, kebab-case only ([a-z][a-z0-9-]*).
• If name is supplied, apply this sanitisation pipeline in order:
  1. Lowercase.
  2. Replace spaces and underscores with -.
  3. Strip any character not in [a-z0-9-].
  4. Strip leading hyphens and leading digits until the name starts with [a-z].
  5. Strip trailing hyphens. Collapse consecutive hyphens to one.
  6. Truncate to 20 chars. If the result is empty after step 6, ask via AskUserQuestion for a valid name instead of emitting an invalid identifier. Warn the user whenever any coercion occurred.
• If name is omitted: auto-generate via the algorithm below. When the result is ambiguous (all-utility list, or generated name is a single token under 4 chars), ask via AskUserQuestion with the generated name pre-filled as the suggestion rather than silently picking.

Auto-name algorithm

1. Tokenise the class string on whitespace. Deduplicate (preserve order).
2. Partition tokens into semantic and utility:
   • Utility prefixes (classify as utility): py-, px-, pt-, pb-, pl-, pr-, mt-, mb-, ml-, mr-, mx-, my-, m-, p-, gap-, text-, bg-, border-, rounded-, w-, h-, min-, max-, flex-, grid-, col-, row-, items-, justify-, self-, place-, order-, z-, opacity-, shadow-, ring-, sr-, not-sr-.
   • Single well-known keywords with no hyphen (e.g. flex, hidden, block, inline) also count as utility.
   • Everything else is semantic.
3. Build the candidate name:
   • Primary: first semantic token. If none, first utility token stripped of any trailing -N numeric suffix.
   • Secondary: first remaining token (semantic preferred over utility) that adds distinct meaning. Skip if combining with primary exceeds 20 chars.
   • Join with -, lowercase. Collapse any double -. Strip leading/trailing -.
4. Truncate to 20 chars (hard limit). If result is empty or ≤ 1 char, use custom-class and warn.

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Workflow

1. Parse input. Accept a pasted HTML snippet or a bare class string (with or without surrounding quotes). Use a regex to extract the class="…" value when HTML is present. Tokenise and deduplicate.

2. Determine the class name. Apply the Name rules above. When auto-generating and the class list is all-utility or the generated name is ambiguous, use AskUserQuestion with the suggestion pre-filled.

3. Discover CSS files. Run:

   find . -name "*.css" -not -path "*/node_modules/*" -not -path "*/.git/*" -not -path "*/dist/*" -not -path "*/build/*"
   

   Collect the resulting file list. If no .css files are found, note this and all tokens will be unresolved.

4. Resolve declarations. For each class token, apply CSS identifier escaping rules to build its selector form before grepping:

   • Escape any character that is not a valid unquoted CSS identifier character: : → \:, & → \&, . → \., % → \%, etc.
   • If the token starts with a digit, apply CSS hex escaping for that leading digit (the hex sequence requires a trailing space as its terminator). For example, 2xl:flex becomes \32 xl\:flex in its selector form, where \32 is the hex escape for 2 and the space terminates the escape sequence. This correctly handles Tailwind variant tokens (hover:bg-red-500 → .hover\:bg-red-500) and breakpoint-prefixed tokens (2xl:* → .\32 xl\:*). Then grep the discovered files for a selector containing .<escaped-token> followed by any of: whitespace, {, ,, or :. Extract the property/value declarations from the matching block.
   • A token is resolved if at least one CSS file contains a matching selector with declarations.
   • A token is unresolved if no match is found — it is a custom or semantic class defined elsewhere (or not yet written).

5. Emit the CSS class block. Output a single class with:

   • Resolved declarations inlined in source order (one property per line).
   • Resolved declarations that appear inside an at-rule (@media, @supports, @layer) in the source file must be emitted with their at-rule wrapper preserved as a nested block — do not strip the context, or the declarations will stop working at the intended breakpoint or feature query. Group multiple tokens that share the same at-rule condition into one nested block.
   • Each unresolved token as a /* <token>: add declarations manually */ placeholder comment, preserving its relative position.

   Example for <div class="testimonial flex-grid py-8 items-center">:

   /* extracted: testimonial flex-grid py-8 items-center */
   .testimonial-grid {
     /* testimonial: add declarations manually */
     /* flex-grid: add declarations manually */
     padding-block: 2rem;
     align-items: center;
   }
   

6. Emit the refactored HTML. Replace the full class="…" value with the new single class name. Preserve all other attributes unchanged (including data-*, id, aria-*).

7. Print a summary:

   • Original class count → 1, name chosen, whether it was provided or auto-generated
   • Resolved: N declarations inlined from project CSS files
   • Unresolved: list any tokens that need manual declarations
   • Any name truncation or kebab-case coercion warnings