CSS Colour change

[ Moderator note: moved to Fixing WordPress. ]

so im having trouble changing colours of some of the elements, basically i want to change everything that is red within the site to my brand colour blue

I realise some of this is within the css somewhere but not sure how to go about it!

Mainly small things such as the ‘buffering wheel’ (not sure what you call it and the small red lines highlighting which page im on are annoying me the most!

Any help appreciated