diff --git a/dev/css-to-json-util.js b/dev/css-to-json-util.js
new file mode 100644
index 00000000..bdcac65b
--- /dev/null
+++ b/dev/css-to-json-util.js
@@ -0,0 +1,169 @@
+/*
+ * Copyright (C) 2021  Yomichan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+const fs = require('fs');
+const css = require('css');
+
+function indexOfRule(rules, selectors) {
+    const jj = selectors.length;
+    for (let i = 0, ii = rules.length; i < ii; ++i) {
+        const ruleSelectors = rules[i].selectors;
+        if (ruleSelectors.length !== jj) { continue; }
+        let okay = true;
+        for (let j = 0; j < jj; ++j) {
+            if (selectors[j] !== ruleSelectors[j]) {
+                okay = false;
+                break;
+            }
+        }
+        if (okay) { return i; }
+    }
+    return -1;
+}
+
+function removeProperty(styles, property, removedProperties) {
+    let removeCount = removedProperties.get(property);
+    if (typeof removeCount !== 'undefined') { return removeCount; }
+    removeCount = 0;
+    for (let i = 0, ii = styles.length; i < ii; ++i) {
+        const key = styles[i][0];
+        if (key !== property) { continue; }
+        styles.splice(i, 1);
+        --i;
+        --ii;
+        ++removeCount;
+    }
+    removedProperties.set(property, removeCount);
+    return removeCount;
+}
+
+function formatRulesJson(rules) {
+    // Manually format JSON, for improved compactness
+    // return JSON.stringify(rules, null, 4);
+    const indent1 = '    ';
+    const indent2 = indent1.repeat(2);
+    const indent3 = indent1.repeat(3);
+    let result = '';
+    result += '[';
+    let index1 = 0;
+    for (const {selectors, styles} of rules) {
+        if (index1 > 0) { result += ','; }
+        result += `\n${indent1}{\n${indent2}"selectors": `;
+        if (selectors.length === 1) {
+            result += `[${JSON.stringify(selectors[0], null, 4)}]`;
+        } else {
+            result += JSON.stringify(selectors, null, 4).replace(/\n/g, '\n' + indent2);
+        }
+        result += `,\n${indent2}"styles": [`;
+        let index2 = 0;
+        for (const [key, value] of styles) {
+            if (index2 > 0) { result += ','; }
+            result += `\n${indent3}[${JSON.stringify(key)}, ${JSON.stringify(value)}]`;
+            ++index2;
+        }
+        if (index2 > 0) { result += `\n${indent2}`; }
+        result += `]\n${indent1}}`;
+        ++index1;
+    }
+    if (index1 > 0) { result += '\n'; }
+    result += ']';
+    return result;
+}
+
+function generateRules(cssFile, cssFileOverrides) {
+    const content1 = fs.readFileSync(cssFile, {encoding: 'utf8'});
+    const content2 = fs.readFileSync(cssFileOverrides, {encoding: 'utf8'});
+    const stylesheet1 = css.parse(content1, {}).stylesheet;
+    const stylesheet2 = css.parse(content2, {}).stylesheet;
+
+    const removePropertyPattern = /^remove-property\s+([a-zA-Z0-9-]+)$/;
+    const removeRulePattern = /^remove-rule$/;
+
+    const rules = [];
+
+    // Default stylesheet
+    for (const rule of stylesheet1.rules) {
+        if (rule.type !== 'rule') { continue; }
+        const {selectors, declarations} = rule;
+        const styles = [];
+        for (const declaration of declarations) {
+            if (declaration.type !== 'declaration') { console.log(declaration); continue; }
+            const {property, value} = declaration;
+            styles.push([property, value]);
+        }
+        if (styles.length > 0) {
+            rules.push({selectors, styles});
+        }
+    }
+
+    // Overrides
+    for (const rule of stylesheet2.rules) {
+        if (rule.type !== 'rule') { continue; }
+        const {selectors, declarations} = rule;
+        const removedProperties = new Map();
+        for (const declaration of declarations) {
+            switch (declaration.type) {
+                case 'declaration':
+                    {
+                        const index = indexOfRule(rules, selectors);
+                        let entry;
+                        if (index >= 0) {
+                            entry = rules[index];
+                        } else {
+                            entry = {selectors, styles: []};
+                            rules.push(entry);
+                        }
+                        const {property, value} = declaration;
+                        removeProperty(entry.styles, property, removedProperties);
+                        entry.styles.push([property, value]);
+                    }
+                    break;
+                case 'comment':
+                    {
+                        const index = indexOfRule(rules, selectors);
+                        if (index < 0) { throw new Error('Could not find rule with matching selectors'); }
+                        const comment = declaration.comment.trim();
+                        let m;
+                        if ((m = removePropertyPattern.exec(comment)) !== null) {
+                            const property = m[1];
+                            const removeCount = removeProperty(rules[index].styles, property, removedProperties);
+                            if (removeCount === 0) { throw new Error(`Property removal is unnecessary; ${property} does not exist`); }
+                        } else if ((m = removeRulePattern.exec(comment)) !== null) {
+                            rules.splice(index, 1);
+                        }
+                    }
+                    break;
+            }
+        }
+    }
+
+    // Remove empty
+    for (let i = 0, ii = rules.length; i < ii; ++i) {
+        if (rules[i].styles.length > 0) { continue; }
+        rules.splice(i, 1);
+        --i;
+        --ii;
+    }
+
+    return rules;
+}
+
+
+module.exports = {
+    formatRulesJson,
+    generateRules
+};
diff --git a/dev/generate-structured-content-style.js b/dev/generate-structured-content-style.js
index 8335efc2..baa1a513 100644
--- a/dev/generate-structured-content-style.js
+++ b/dev/generate-structured-content-style.js
@@ -17,151 +17,13 @@
 
 const fs = require('fs');
 const path = require('path');
-const css = require('css');
 const {testMain} = require('./util');
-
-function indexOfRule(rules, selectors) {
-    const jj = selectors.length;
-    for (let i = 0, ii = rules.length; i < ii; ++i) {
-        const ruleSelectors = rules[i].selectors;
-        if (ruleSelectors.length !== jj) { continue; }
-        let okay = true;
-        for (let j = 0; j < jj; ++j) {
-            if (selectors[j] !== ruleSelectors[j]) {
-                okay = false;
-                break;
-            }
-        }
-        if (okay) { return i; }
-    }
-    return -1;
-}
-
-function removeProperty(styles, property, removedProperties) {
-    let removeCount = removedProperties.get(property);
-    if (typeof removeCount !== 'undefined') { return removeCount; }
-    removeCount = 0;
-    for (let i = 0, ii = styles.length; i < ii; ++i) {
-        const key = styles[i][0];
-        if (key !== property) { continue; }
-        styles.splice(i, 1);
-        --i;
-        --ii;
-        ++removeCount;
-    }
-    removedProperties.set(property, removeCount);
-    return removeCount;
-}
-
-function formatRulesJson(rules) {
-    // Manually format JSON, for improved compactness
-    // return JSON.stringify(rules, null, 4);
-    const indent1 = '    ';
-    const indent2 = indent1.repeat(2);
-    const indent3 = indent1.repeat(3);
-    let result = '';
-    result += '[';
-    let index1 = 0;
-    for (const {selectors, styles} of rules) {
-        if (index1 > 0) { result += ','; }
-        result += `\n${indent1}{\n${indent2}"selectors": `;
-        if (selectors.length === 1) {
-            result += `[${JSON.stringify(selectors[0], null, 4)}]`;
-        } else {
-            result += JSON.stringify(selectors, null, 4).replace(/\n/g, '\n' + indent2);
-        }
-        result += `,\n${indent2}"styles": [`;
-        let index2 = 0;
-        for (const [key, value] of styles) {
-            if (index2 > 0) { result += ','; }
-            result += `\n${indent3}[${JSON.stringify(key)}, ${JSON.stringify(value)}]`;
-            ++index2;
-        }
-        if (index2 > 0) { result += `\n${indent2}`; }
-        result += `]\n${indent1}}`;
-        ++index1;
-    }
-    if (index1 > 0) { result += '\n'; }
-    result += ']';
-    return result;
-}
+const {formatRulesJson, generateRules: generateRulesGeneric} = require('./css-to-json-util');
 
 function generateRules() {
-    const content1 = fs.readFileSync(path.join(__dirname, '..', 'ext/css/structured-content.css'), {encoding: 'utf8'});
-    const content2 = fs.readFileSync(path.join(__dirname, 'data/structured-content-overrides.css'), {encoding: 'utf8'});
-    const stylesheet1 = css.parse(content1, {}).stylesheet;
-    const stylesheet2 = css.parse(content2, {}).stylesheet;
-
-    const removePropertyPattern = /^remove-property\s+([a-zA-Z0-9-]+)$/;
-    const removeRulePattern = /^remove-rule$/;
-
-    const rules = [];
-
-    // Default stylesheet
-    for (const rule of stylesheet1.rules) {
-        if (rule.type !== 'rule') { continue; }
-        const {selectors, declarations} = rule;
-        const styles = [];
-        for (const declaration of declarations) {
-            if (declaration.type !== 'declaration') { console.log(declaration); continue; }
-            const {property, value} = declaration;
-            styles.push([property, value]);
-        }
-        if (styles.length > 0) {
-            rules.push({selectors, styles});
-        }
-    }
-
-    // Overrides
-    for (const rule of stylesheet2.rules) {
-        if (rule.type !== 'rule') { continue; }
-        const {selectors, declarations} = rule;
-        const removedProperties = new Map();
-        for (const declaration of declarations) {
-            switch (declaration.type) {
-                case 'declaration':
-                    {
-                        const index = indexOfRule(rules, selectors);
-                        let entry;
-                        if (index >= 0) {
-                            entry = rules[index];
-                        } else {
-                            entry = {selectors, styles: []};
-                            rules.push(entry);
-                        }
-                        const {property, value} = declaration;
-                        removeProperty(entry.styles, property, removedProperties);
-                        entry.styles.push([property, value]);
-                    }
-                    break;
-                case 'comment':
-                    {
-                        const index = indexOfRule(rules, selectors);
-                        if (index < 0) { throw new Error('Could not find rule with matching selectors'); }
-                        const comment = declaration.comment.trim();
-                        let m;
-                        if ((m = removePropertyPattern.exec(comment)) !== null) {
-                            const property = m[1];
-                            const removeCount = removeProperty(rules[index].styles, property, removedProperties);
-                            if (removeCount === 0) { throw new Error(`Property removal is unnecessary; ${property} does not exist`); }
-                        } else if ((m = removeRulePattern.exec(comment)) !== null) {
-                            rules.splice(index, 1);
-                        }
-                    }
-                    break;
-            }
-        }
-    }
-
-    // Remove empty
-    for (let i = 0, ii = rules.length; i < ii; ++i) {
-        if (rules[i].styles.length > 0) { continue; }
-        rules.splice(i, 1);
-        --i;
-        --ii;
-    }
-
-    return rules;
+    const cssFile = path.join(__dirname, '..', 'ext/css/structured-content.css');
+    const cssFileOverrides = path.join(__dirname, 'data/structured-content-overrides.css');
+    return generateRulesGeneric(cssFile, cssFileOverrides);
 }
 
 function generateRulesJson() {