How does line-height vertically center text?

Question

I\'m trying to understand why the line-height CSS property places the text vertically in the middle of this button:

Answer 1

line-height defines the height of text which make the paragraph looks neat so vertical-align works with respect to line-height when you increase the line height it increases the height and the you can more clearly see the effects of vertical-alignment of text

think this as a notebook which we children use to learn English -writing in nursery class