Tool-bar separator not centered and too light

[mrleblanc101]

Hi,
Toolbar separator are not center and are too dim using atom-material-ui (see screenshot).
I had to add this to my stylesheet to have the expected behavior:

.amu-compact-tab-bar .tool-bar.tool-bar-16px.tool-bar-vertical .tool-bar-spacer,
.amu-compact-tab-bar .tool-bar.tool-bar-24px.tool-bar-vertical .tool-bar-spacer,
.amu-compact-tab-bar .tool-bar.tool-bar-32px.tool-bar-vertical .tool-bar-spacer {
margin: 0 auto;
border-color: rgba(131, 148, 150, 0.65);
}

Reproduction Steps:

1. Install atom material-ui
2. Enable solarized-dark syntax
3. Set tool-bar position to vertical

Expected behavior:

The tool-bar separator should be centered when using the vertical tool-bar position

Observed behavior:

The tool-bar separator are left aligned (margin: 0.5em 0 instead of 0.5em auto)

Screenshots and GIFs

Atom version: 1.23
OS and version: macOS 10.13.3