const CSSPath = 'https://iwb.jp/s/common.css'
const insertRuleCode = `
h1 {
color: red;
}
#footer a {
color: orange;
}
`.replaceAll('}', '}}').split(/}\n/).filter(String)
for (let stylesheet of document.styleSheets) {
if (stylesheet.href && (stylesheet.href).match(/[^\?]+/)[0] === CSSPath) {
for (let insertRuleText of insertRuleCode) {
stylesheet.insertRule(insertRuleText, stylesheet.cssRules.length)
}
break
}
}