Mobile web development - Keyboard popup affect the height

When text box is clicked, soft keyboard is popped up and it breaks the whole CSS structure.

For example, I am trying to give 70% of height from device. But when keyboard is up, the 70% is re calculated from the rest of space on screen except keyboard area.

How can I keep the height even if the keyboard is up? I would like to use something like '%', 'vh' but I don't want to use 'px', 'em'..