A modern website has the content separate to the formatting. CSS is the markup language used in the U3A Tauranga website.
Where is the file and can it be changed?
Access the file from the adminstrator (back end) log in. Extentions - Templates
Click on Templates
Then select the template, at present Basetemplate-joomla3.
The Template files that control the layout of the website, including CSS files, are then accessable.
The CSS file in use as at April 2016 is templateU3A.css.
The file opens in a small window, suitable for simple editing or to paste a prepared segment into the file
Alternative Method
If you are familiar with using a localhost for website development the CSS file is accessable for direct editing using a text editor of your choice.
From the folder, htdocs, (www or whatever folder is setup to hold the local copy of the web site files) navigate to the website you are using for testing, within the templates folder will be the CSS files used by the website.
Open the templatesU3A.css file in a text editor of your choice. It is a lot easier to navigate, you can use 'find' to locate values or search and replace if you want to change a colour value over the whole website.
After the changes have been checked and correct either paste in a section to add to the CSS file. replace a section or replace the whole file.