Sources page - css massage - sticky header, label normalization, change button styling to the component buttons

[zoobot]

From @tzinckgraf
"for the tree data, do we want a sticky header so that the Search stays at the top?
for the source data, we might want to style the buttons a little bit. the dark green with the black writing is a little hard to read. we might also want some tooltips on the source data to help people know what to put where. for example, Info URL vs Source URL. also, we should be consistent with naming, such as URL vs Url."

• sticky header
• label normalization
• change button styling to the component buttons