Click to Tweets allow you to place quotes within your posts that encourage users to share those quotes directly onto Twitter with a link back to your site.
In this section of the settings, you can select from several pre-configured visual styles. As you browse available styles, the example Click to Tweet below the select box will update in real-time to show you how it will look in your posts.
If you have selected Create Your Own CSS in Your Theme, you can write in your own custom-coded styles for the Click To Tweet. Here are some of the selectors you might want to use:
The top-most parent selector is:
The inner text selector is:
The button text is:
And the Twitter icon is: