fix nav bar in 404 page

[ydcjeff]

Describe the bug

Nav bar became too large in 404 page and covered the h1 title.

Expected result

NavBar not covered the h1 title.

Reproduction

https://code-generator.pytorch-ignite.ai/foobar

Steps to reproduce

View the reproduction link on mobile

[B1TSH3LL]

I Can Work On This Issue Please Assign It To Me :)

[rwiteshbera]

I can work on this issue, can you please assign me this issue? @ydcjeff