Fix #11909: make footer responsive in smaller view (#12234)
Fix #11909: make footer responsive in smaller view (#12234)

* make footer align center

* made footer responsive

* rm redundant chnages
oppia/oppia,kevinlee12/oppia,brianrodri/oppia,oppia/oppia,brianrodri/oppia,oppia/oppia,kevinlee12/oppia,brianrodri/oppia,kevinlee12/oppia,oppia/oppia,brianrodri/oppia,kevinlee12/oppia,kevinlee12/oppia,oppia/oppia,brianrodri/oppia