Twitter is dynamically generated
This means that the HTML that is loaded when you request the HTML does not contain any tweets. Once the basic HTML has loaded, then the tweets begin to get populated into the page via JavaScript.
Since this is the case, any HTML you recieve from IMPORTXML will not have any tweets. Twitter itself tries to limit any scraping that is not done via the API.
So unfortunately your best recourse is to either use the API (it has a free tier), or learn to use some web automation software such as Puppeteer, which can emulate a person who visits the site, waits for a second to let the content load, and then scrape the data.
Disclaimer: It is possible that IMPORTXML will work using the css class as you have done, though this will be very unreliable. The CSS classes are also auto generated, so they will be changing very often.
Demonstration
Using curl on the command line to fetch the raw HTML of https://twitter.com/Twitter/status/1380306486962782208 (before any JavaScript changes):
curl https://twitter.com/Twitter/status/1380306486962782208 >> twitter.html
Examining the resulting twitter.html file:
<!DOCTYPE html>
<html dir="ltr" lang="en">
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width,initial-scale=1,maximum-scale=1,user-scalable=0,viewport-fit=cover" />
<link rel="preconnect" href="//abs.twimg.com" />
<link rel="dns-prefetch" href="//abs.twimg.com" />
<link rel="preconnect" href="//api.twitter.com" />
<link rel="dns-prefetch" href="//api.twitter.com" />
<link rel="preconnect" href="//pbs.twimg.com" />
<link rel="dns-prefetch" href="//pbs.twimg.com" />
<link rel="preconnect" href="//t.co" />
<link rel="dns-prefetch" href="//t.co" />
<link rel="preconnect" href="//video.twimg.com" />
<link rel="dns-prefetch" href="//video.twimg.com" />
<link rel="preload" as="script" crossorigin="anonymous" href="https://abs.twimg.com/responsive-web/client-web-legacy/polyfills.98da7185.js" nonce="MjE5MTk0YTItNjQxMy00NzhjLWE0ZWEtNTA0NzEwMzdkNmQy" />
<link rel="preload" as="script" crossorigin="anonymous" href="https://abs.twimg.com/responsive-web/client-web-legacy/vendors~main.6fa4fac5.js" nonce="MjE5MTk0YTItNjQxMy00NzhjLWE0ZWEtNTA0NzEwMzdkNmQy" />
<link rel="preload" as="script" crossorigin="anonymous" href="https://abs.twimg.com/responsive-web/client-web-legacy/i18n/en.2eb8dfe5.js" nonce="MjE5MTk0YTItNjQxMy00NzhjLWE0ZWEtNTA0NzEwMzdkNmQy" />
<link rel="preload" as="script" crossorigin="anonymous" href="https://abs.twimg.com/responsive-web/client-web-legacy/main.88d8e8e5.js" nonce="MjE5MTk0YTItNjQxMy00NzhjLWE0ZWEtNTA0NzEwMzdkNmQy" />
<meta property="fb:app_id" content="2231777543" />
<meta property="og:site_name" content="Twitter" />
<meta name="google-site-verification" content="acYOOcR5z6puMzLn6hLDZI1nNHXPxt57OIstz1vnCV0" />
<meta name="facebook-domain-verification" content="x6sdcc8b5ju3bh8nbm59eswogvg6t1" />
<link rel="manifest" href="/manifest.json" crossOrigin="use-credentials" />
<link rel="alternate" hreflang="x-default" href="https://twitter.com/twitter/status/1380306486962782208" />
<link rel="alternate" hreflang="en" href="https://twitter.com/twitter/status/1380306486962782208?lang=en" />
<link rel="alternate" hreflang="ar" href="https://twitter.com/twitter/status/1380306486962782208?lang=ar" />
<link rel="alternate" hreflang="ar-x-fm" href="https://twitter.com/twitter/status/1380306486962782208?lang=ar-x-fm" />
<link rel="alternate" hreflang="bg" href="https://twitter.com/twitter/status/1380306486962782208?lang=bg" />
<link rel="alternate" hreflang="bn" href="https://twitter.com/twitter/status/1380306486962782208?lang=bn" />
<link rel="alternate" hreflang="ca" href="https://twitter.com/twitter/status/1380306486962782208?lang=ca" />
<link rel="alternate" hreflang="cs" href="https://twitter.com/twitter/status/1380306486962782208?lang=cs" />
<link rel="alternate" hreflang="da" href="https://twitter.com/twitter/status/1380306486962782208?lang=da" />
<link rel="alternate" hreflang="de" href="https://twitter.com/twitter/status/1380306486962782208?lang=de" />
<link rel="alternate" hreflang="el" href="https://twitter.com/twitter/status/1380306486962782208?lang=el" />
<link rel="alternate" hreflang="en-GB" href="https://twitter.com/twitter/status/1380306486962782208?lang=en-GB" />
<link rel="alternate" hreflang="en-ss" href="https://twitter.com/twitter/status/1380306486962782208?lang=en-ss" />
<link rel="alternate" hreflang="en-xx" href="https://twitter.com/twitter/status/1380306486962782208?lang=en-xx" />
<link rel="alternate" hreflang="es" href="https://twitter.com/twitter/status/1380306486962782208?lang=es" />
<link rel="alternate" hreflang="eu" href="https://twitter.com/twitter/status/1380306486962782208?lang=eu" />
<link rel="alternate" hreflang="fa" href="https://twitter.com/twitter/status/1380306486962782208?lang=fa" />
<link rel="alternate" hreflang="fi" href="https://twitter.com/twitter/status/1380306486962782208?lang=fi" />
<link rel="alternate" hreflang="fil" href="https://twitter.com/twitter/status/1380306486962782208?lang=fil" />
<link rel="alternate" hreflang="fr" href="https://twitter.com/twitter/status/1380306486962782208?lang=fr" />
<link rel="alternate" hreflang="ga" href="https://twitter.com/twitter/status/1380306486962782208?lang=ga" />
<link rel="alternate" hreflang="gl" href="https://twitter.com/twitter/status/1380306486962782208?lang=gl" />
<link rel="alternate" hreflang="gu" href="https://twitter.com/twitter/status/1380306486962782208?lang=gu" />
<link rel="alternate" hreflang="he" href="https://twitter.com/twitter/status/1380306486962782208?lang=he" />
<link rel="alternate" hreflang="hi" href="https://twitter.com/twitter/status/1380306486962782208?lang=hi" />
<link rel="alternate" hreflang="hr" href="https://twitter.com/twitter/status/1380306486962782208?lang=hr" />
<link rel="alternate" hreflang="hu" href="https://twitter.com/twitter/status/1380306486962782208?lang=hu" />
<link rel="alternate" hreflang="id" href="https://twitter.com/twitter/status/1380306486962782208?lang=id" />
<link rel="alternate" hreflang="it" href="https://twitter.com/twitter/status/1380306486962782208?lang=it" />
<link rel="alternate" hreflang="ja" href="https://twitter.com/twitter/status/1380306486962782208?lang=ja" />
<link rel="alternate" hreflang="kn" href="https://twitter.com/twitter/status/1380306486962782208?lang=kn" />
<link rel="alternate" hreflang="ko" href="https://twitter.com/twitter/status/1380306486962782208?lang=ko" />
<link rel="alternate" hreflang="mr" href="https://twitter.com/twitter/status/1380306486962782208?lang=mr" />
<link rel="alternate" hreflang="ms" href="https://twitter.com/twitter/status/1380306486962782208?lang=ms" />
<link rel="alternate" hreflang="nb" href="https://twitter.com/twitter/status/1380306486962782208?lang=nb" />
<link rel="alternate" hreflang="nl" href="https://twitter.com/twitter/status/1380306486962782208?lang=nl" />
<link rel="alternate" hreflang="pl" href="https://twitter.com/twitter/status/1380306486962782208?lang=pl" />
<link rel="alternate" hreflang="pt" href="https://twitter.com/twitter/status/1380306486962782208?lang=pt" />
<link rel="alternate" hreflang="ro" href="https://twitter.com/twitter/status/1380306486962782208?lang=ro" />
<link rel="alternate" hreflang="ru" href="https://twitter.com/twitter/status/1380306486962782208?lang=ru" />
<link rel="alternate" hreflang="sk" href="https://twitter.com/twitter/status/1380306486962782208?lang=sk" />
<link rel="alternate" hreflang="sr" href="https://twitter.com/twitter/status/1380306486962782208?lang=sr" />
<link rel="alternate" hreflang="sv" href="https://twitter.com/twitter/status/1380306486962782208?lang=sv" />
<link rel="alternate" hreflang="ta" href="https://twitter.com/twitter/status/1380306486962782208?lang=ta" />
<link rel="alternate" hreflang="th" href="https://twitter.com/twitter/status/1380306486962782208?lang=th" />
<link rel="alternate" hreflang="tr" href="https://twitter.com/twitter/status/1380306486962782208?lang=tr" />
<link rel="alternate" hreflang="uk" href="https://twitter.com/twitter/status/1380306486962782208?lang=uk" />
<link rel="alternate" hreflang="ur" href="https://twitter.com/twitter/status/1380306486962782208?lang=ur" />
<link rel="alternate" hreflang="vi" href="https://twitter.com/twitter/status/1380306486962782208?lang=vi" />
<link rel="alternate" hreflang="zh" href="https://twitter.com/twitter/status/1380306486962782208?lang=zh" />
<link rel="alternate" hreflang="zh-Hant" href="https://twitter.com/twitter/status/1380306486962782208?lang=zh-Hant" />
<link rel="canonical" href="https://twitter.com/twitter/status/1380306486962782208" />
<link rel="search" type="application/opensearchdescription+xml" href="/opensearch.xml" title="Twitter">
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与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
