So PAGE_CONTAINER is a template we can almost all expect to see outdated every single release if you edit it. I'll post a workaround at the end but essentially it means that you've made an adjustment to the template and the parent has since been updated. Long story short... you need to re-apply your edits to the parent version of the template.
Ready for a long wall of text
In this example, my PAGE_CONTAINER is outdated, click "View custom changes" top right.
Scrolling down you'll see what changes I've added by what's in green:
This is a custom link I added, so I made a change on the template which has since been updated as I mentioned. Scrolling further down...
Red lines are what can be found in the parent style currently, with a red line directly below with almost the same content it means a change was made inside the line of code itself. Essentially here I'd copy the red line and go replace the green line directly below.
If you see a red line of code with nothing below it, it means that it's new code being added entirely so you just need to add it in the correct place.
Solutions / tools: NotePad++ NotePad++ is a nice text editor which has abilities to add plugins, one of which is a compare tool. Often what I'll do is simply copy the entire contents of my custom outdated template, paste it into notepad++, then click revert on the template. Next, I'll go back into the template, open it (it's now up-to-date but has lost all your custom changes) and paste that into a new file on notepad++.
It'll look like this when comparing:
Left side is my custom template, the right side of the parent version that we reverted too. I can simply copy the code over easily and continue with my edits. When I'm all done simply take the right side, copy and paste it back into the PAGE_CONTAINER template.
While template modifications aren't necessarily meant for styling (although I wish they would make it so) you can use them to avoid outdated templates.
This finds the current navigation link and adds in our custom link automatically.
I hope this helps... the fix for outdated templates is simply not a go here and do this type of solution. Sorry for the wall of text, I'll make work this into a sticky thread for everyone.