I\'m trying to customise the new Twitter widget, but having some problems with the CSS and can\'t seem to override theirs on this new one. I\'ve tried searching for solution
I don't know if it was possible back then when the question was asked, but now it is, check the docs:
<a class="twitter-timeline" data-chrome="nofooter" ....">Tweets</a>
They create an iframe, so it is another document.
You cannot style elements in another document, so it is not possible unless twitter provides a hook to embed your own stylesheet in their iframe..
Twitter only allows to style the link color of the widget and pick a light/dark theme.
Alternatively, you can create your own widget by using the twitter API and then you can style it anyway you want..