html - bootstrap sub-pixels on resize -

I have two rows on a bootstrap in one line, I have a button, and on the second line, there is a text field .

Here is the code for them (Z)

  .row: .col-xs-12: input.form-control (type = 'text' required placeholder = ' Question '). Oo: .col-xs-4.col-xs-offset-8: input.btn.btn-primary .btn-block (type =' submit 'value =' add ')  

The problem is that depending on the viewport size (such as resizing the browser), the elements sometimes happen, the situation is wrong, such as half pixels too much or too little to see the following pictures Understand what I am saying.