Stick footer to the bottom

[php-coder]

• https://philipwalton.github.io/solved-by-flexbox/demos/sticky-footer/
• https://habr.com/ru/post/511612/ (in Russian) or https://moderncss.dev/keep-the-footer-at-the-bottom-flexbox-vs-grid/ (in English)
• https://dev.to/5t3ph/keep-the-footer-at-the-bottom-flexbox-vs-grid-4o2o

[php-coder]

From my notes: use flex-shrink: 0 (and flex-grow: 1; flex: 1 0 auto;) to make a footer stick to the bottom

[php-coder]

NOTE: don't forget to update error pages during deploy.