Various style fixes

[svbergerem]

• Supersedes Using character (×) instead of asset for publisher close button #5332
• Fixes the close button for popovers
• Removes bootstrap_header_padding which no longer had any effect
• Removes the second #hide_location button from the publisher. We only had it for blueprint compatibility and didn't display it in the bootstrap publisher.
• Improves style of getting started message

old:

new:

[jhass]

Thank you!