ARROW-4775: [Site] Site navbar cannot be expanded
ARROW-4775: [Site] Site navbar cannot be expanded

I found that the navbar at the top of the page cannot be expanded when the page is narrow.
This pull request fixes this problem.

Author: Kenta Murata <mrkn@mrkn.jp>

Closes #3814 from mrkn/fix_site_navbar_expanding_behavior and squashes the following commits:

8fb38ac0 <Kenta Murata>  Fix navbar expanding behavior

majetideepak/arrow,renesugar/arrow,itaiin/arrow,cpcloud/arrow,icexelloss/arrow,xhochy/arrow,majetideepak/arrow,majetideepak/arrow,itaiin/arrow,kou/arrow,cpcloud/arrow,renesugar/arrow,xhochy/arrow,apache/arrow,wesm/arrow,cpcloud/arrow,cpcloud/arrow,icexelloss/arrow,itaiin/arrow,renesugar/arrow,tebeka/arrow,majetideepak/arrow,apache/arrow,cpcloud/arrow,icexelloss/arrow,apache/arrow,renesugar/arrow,kou/arrow,xhochy/arrow,icexelloss/arrow,itaiin/arrow,xhochy/arrow,cpcloud/arrow,wesm/arrow,xhochy/arrow,xhochy/arrow,wesm/arrow,wesm/arrow,tebeka/arrow,renesugar/arrow,majetideepak/arrow,apache/arrow,icexelloss/arrow,cpcloud/arrow,kou/arrow,xhochy/arrow,laurentgo/arrow,xhochy/arrow,renesugar/arrow,tebeka/arrow,itaiin/arrow,itaiin/arrow,apache/arrow,laurentgo/arrow,tebeka/arrow,apache/arrow,laurentgo/arrow,apache/arrow,itaiin/arrow,apache/arrow,apache/arrow,laurentgo/arrow,majetideepak/arrow,wesm/arrow,icexelloss/arrow,renesugar/arrow,wesm/arrow,majetideepak/arrow,laurentgo/arrow,itaiin/arrow,laurentgo/arrow,xhochy/arrow,itaiin/arrow,laurentgo/arrow,itaiin/arrow,kou/arrow,apache/arrow,kou/arrow,majetideepak/arrow,laurentgo/arrow,icexelloss/arrow,tebeka/arrow,laurentgo/arrow,renesugar/arrow,icexelloss/arrow,icexelloss/arrow,renesugar/arrow,icexelloss/arrow,cpcloud/arrow,icexelloss/arrow,kou/arrow,itaiin/arrow,itaiin/arrow,majetideepak/arrow,majetideepak/arrow,cpcloud/arrow,kou/arrow,wesm/arrow,icexelloss/arrow,cpcloud/arrow,renesugar/arrow,laurentgo/arrow,xhochy/arrow,majetideepak/arrow,icexelloss/arrow,majetideepak/arrow,laurentgo/arrow,wesm/arrow,kou/arrow,kou/arrow,renesugar/arrow,itaiin/arrow,majetideepak/arrow,itaiin/arrow,apache/arrow,xhochy/arrow,itaiin/arrow,renesugar/arrow,cpcloud/arrow,renesugar/arrow,xhochy/arrow,wesm/arrow,kou/arrow,kou/arrow,kou/arrow,apache/arrow,renesugar/arrow,tebeka/arrow,laurentgo/arrow,tebeka/arrow,xhochy/arrow,wesm/arrow,xhochy/arrow,apache/arrow,cpcloud/arrow,wesm/arrow,xhochy/arrow,renesugar/arrow,wesm/arrow,tebeka/arrow,apache/arrow,kou/arrow,tebeka/arrow,cpcloud/arrow,wesm/arrow,wesm/arrow,cpcloud/arrow,majetideepak/arrow,laurentgo/arrow,laurentgo/arrow,icexelloss/arrow,majetideepak/arrow,tebeka/arrow,kou/arrow,laurentgo/arrow