Html&css--line-height is set to height so that the text is centered __html

The first line height is the character size of the text and the margin of the character up and down, the key is that the upper and lower margins are equal, you can think of row height is two invisible horizontal parallel, and in parallel, characters and parallel lines up and down the margin is always the same, that is, vertically centered meaning.

and Height This property is the height of the box properties, the box is not as high as the line to the top and bottom margin is equal to the requirements. But the default in the upper left corner

so is not the line high line-height and the text high height can make the text centered, but should be so understanding, the character is in line height vertically centered, but the row high and the text box height range, resulting in the box can not be vertically centered, If we put the line high line-height and the height of the box set to the same size, meaning that the line is high parallel lines and the upper and lower sides of the box coincide, when the characters are still in the height of the vertical center, but also conveniently in the box vertically in the center.