是的。你用得对。极其好！但是要记得＂及＂跟＂极＂还不同。

你用的对。但“极其”“很”“挺”不完全一样。语气轻重程度不一样。“我极其高兴 ”，“我很高兴”，“我挺高兴”这三个句子都对。但是第一个语气最强，第二个语气强于第三个。

哎哟！我打字的时候打错了。　不好好意思。

It is "極"其 (simplified: "极"其), not "及"其. Yes, it applies to every case just like 很 and 挺; however, 很 and 挺 are much more colloquially used (極其 would be much applied to when it comes to writing/composition). Here I want to note another phrase, 其極 (simplified: 其极), such as 無所不用其極, which means "(to do something) by all means".