[css] Circle button css

Here is a flat design circle button:

enter image description here

_x000D_
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.btn {_x000D_
  height: 80px;_x000D_
  line-height: 80px;  _x000D_
  width: 80px;  _x000D_
  font-size: 2em;_x000D_
  font-weight: bold;_x000D_
  border-radius: 50%;_x000D_
  background-color: #4CAF50;_x000D_
  color: white;_x000D_
  text-align: center;_x000D_
  cursor: pointer;_x000D_
}
_x000D_
<div class="btn">+</div>
_x000D_
_x000D_
_x000D_

but the problem is that the + might not be perfectly centered vertically in all browsers / platforms, because of font differences... see also this question (and its answer): Vertical alignement of span inside a div when the font-size is big