cleaned up redundant css icon code

* redundant code is cleaned up
* added `margin-top: -1;` to menu icons, which positions them 1 pixel
higher than before

Rules
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* **inline icons** should have `line-height: 1;` and be positioned 1
pixel lower than where they are initially positioned
* **floating icons** should have line-height unchanged and be positioned
1 pixel higher than where they are initially positioned