I am a new user to Target, and would like to know is it possible to test one element across an entire site. Scenario: We have a register button in a header on every page is it possible to change the colour of this button globally Instead of changing a button colour on every individual page?
Most definitely! You need to start by choosing single page to setup/compose your test with the visual experience composer (VEC). But then you can layer on a "template" rule to allow a set of urls to qualify for entry in the test.
Configure (gear icon) > page delivery > add template rule with "OR" condition.
For a global test on a site usually something like domain contains mysite.com sould work.
Many thanks for the answer you have saved me a lot of work.