css3 写了一个可伸缩的搜索表单，可是伸长之后有一个框？

Question

搜索表单伸长之后，chrome浏览器上出现一个框（见图），firefox浏览器正常，是什么原因？解决办法是？

Answer 1

It should be the focus style that comes with the browser
You can try it

input {outline:0};

Answer 2

Damn it, I have to guess the code you wrote again

Let’s see if it’s due to focus and outline