Full width inputs in the Search/Replace modal bars

I used flexbox to make the Search and Replace inputs fill the remaining space of the modal bar and shrink/stretch when required.

To @larz to check the final result.

@SAPlayer This time it does works with other languages since it doesn't implies the widths of the buttons. It still doesn't split into multiple lines. I guess it might be possible adding an additional class in JavaScript. I don't think it could be achieved in CSS only.