Best way to center a on a page vertically and horizontally? [duplicate]

Answer 1

position: absolute;
left: 50%;
top: 50%;
-webkit-transform: translate(-50%, -50%);
-ms-transform: translate(-50%, -50%);
transform: translate(-50%, -50%);

Explanation:

Give it an absolute positioning (the parent should have relative positioning). Then, the upper left corner is moved to the center. Because you don't know the width/height yet, you use css transform to translate the position relatively to the middle. translate(-50%, -50%) does reduce the x and y position of the upper left corner by 50% of width and height.