Source control is a saviour for this shit. Can't count the times I've made a small change and completely fucked up the CSS in 20 other files I didn't realise existed...
!important This is my work nightmare, but for side projects I use elm and elm-ui and I just don't need css. So nice, so stable, so robust, so eeeeeasy to maintain. It's genuinely a delight. Boss nopes out when he sees all the whitespace, though, as if semicolons were the only thing keeping things sane.
I use it for web apps rather than plain pages, and you can certainly use it with your existing css, and you can roll new css in a clean and non-clashy way with elm-css, but, like I say, elm-ui lets you RELIABLY build your ui.
Thanks for reminding me about the outdated as fuck HTML/CSS template I need to continue updating tomorrow at work. Might just drink another glass of gin tonight.
Not even a programmer, I'm just a lowly support engineer that barely gets over minimum wage. UK wages suck but this is why I don't try very hard anymore. I have job security by not being incompetent. Only risk of losing it is if they get rid of almost everyone.