Aligning Site Title and Tag line

The title and tagline are aligned by the edge of the character plus its sidebearing (that’s the built-in space that surrounds a letter and is actually part of its design) so I assume that, as you've used a larger font for the title, you want to close the visual indentation.

You should be able to do this by adding this some margin to the tagline. For example, you could add 3px (or your choice of margin) by adding this CSS to Design > Custom CSS:

.Header-tagline {
  margin-left: 3px;
}