It appears that the repository has undergone several changes and renamings:

backend/node_modules/postcss/lib/warning.js

@@ -1,37 +0,0 @@
-'use strict'
-
-class Warning {
-  constructor(text, opts = {}) {
-    this.type = 'warning'
-    this.text = text
-
-    if (opts.node && opts.node.source) {
-      let range = opts.node.rangeBy(opts)
-      this.line = range.start.line
-      this.column = range.start.column
-      this.endLine = range.end.line
-      this.endColumn = range.end.column
-    }
-
-    for (let opt in opts) this[opt] = opts[opt]
-  }
-
-  toString() {
-    if (this.node) {
-      return this.node.error(this.text, {
-        index: this.index,
-        plugin: this.plugin,
-        word: this.word
-      }).message
-    }
-
-    if (this.plugin) {
-      return this.plugin + ': ' + this.text
-    }
-
-    return this.text
-  }
-}
-
-module.exports = Warning
-Warning.default = Warning