Add CSS.escape() to DOM searching chapter

還沒有人認領這個 Issue。

Hello, I was wondering if it would be worth adding something in the chapter _Searching: getElement, querySelector_ about how to pass a variable through `document.querySelector` by using `CSS.escape()`, ie `document.querySelector('div.' + CSS.escape(userColor))`

I write this because I just spent a while trying template literals, etc, and I had no idea CSS.escape() existed and is necessary to do this.

It's probably pretty uncommon to need to pass variables to querySelector, but if anyone else thinks it's worth adding I would be happy to make a PR.

[https://developer.mozilla.org/en-US/docs/Web/API/CSS/escape](url)

首先定位 issue 中提到的「Searching: getElement, querySelector」章節，並檢視其中現有的 querySelector 範例。查看連結的 MDN CSS.escape() 參考資料以取得準確的指引；完成的標準是該章節清楚說明如何安全地將變數傳遞給 querySelector，並包含一個合適的範例。

由索引模型根據 Issue 內容生成。