add initial marp implementation with sample content and build configuration

node_modules/@marp-team/marpit/lib/postcss/root/increasing_specificity.js

@@ -0,0 +1,27 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.rootIncreasingSpecificity = exports.pseudoClass = exports.default = void 0;
+var _postcss_plugin = _interopRequireDefault(require("../../helpers/postcss_plugin"));
+function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
+/** @module */
+
+const pseudoClass = exports.pseudoClass = ':marpit-root';
+const matcher = new RegExp(`\\b(?:section)?${pseudoClass}\\b`, 'g');
+
+/**
+ * Marpit PostCSS root increasing specificity plugin.
+ *
+ * Replace specific pseudo-class selector to `:where(section):not([\20 root])`,
+ * to increase specificity. `:marpit-root` is always added to `section` selector
+ * by root replace plugin so `:where(section):not([\20 root])` must always match
+ * too (HTML does not allow U+0020 SPACE in the attribute name.).
+ *
+ * @function rootIncreasingSpecificity
+ */
+const rootIncreasingSpecificity = exports.rootIncreasingSpecificity = (0, _postcss_plugin.default)('marpit-postcss-root-increasing-specificity', () => css => css.walkRules(rule => {
+  rule.selectors = rule.selectors.map(selector => selector.replace(matcher, ':where(section):not([\\20 root])'));
+}));
+var _default = exports.default = rootIncreasingSpecificity;