Decreased border size to make thin lines

Issue: https://gitlab.e.foundation/e/infra/backlog/-/issues/1018

What is the current behavior?

Right now the horizontal lines seem to be using about 2 or 3 pixels width, which is too much. We need to decrease it to 1 pixel.

There's also a vertical line between the side menu and the files list. That line is also needs to be turned down to 1 pixel.

What is the improved behavior?

• Decrease divider width to 1 pixel for all horizontal dividers (in all pages).
• Decrease side menu horizontal divider width to 1 pixel (reflect the change in all screens too)

What does it bring?

Improved UI.