Block centered of the page

/* SASS version */
/* Negative indent */
.parent
  width: 100%
  height: 100%
  position: absolute
  top: 0
  left: 0
  overflow: auto
.block 
  width: 250px
  height: 250px
  position: absolute
  top: 50%
  left: 50%
  margin: -125px 0 0 -125px
  img 
    max-width: 100%
    height: auto
    display: block
    margin: 0 auto
    border: none
        
/* Automatic indentation */
.parent
  width: 100%
  height: 100%
  position: absolute
  top: 0
  left: 0
  overflow: auto
.block
  width: 250px
  height: 250px
  position: absolute
  top: 0
  right: 0
  bottom: 0
  left: 0
  margin: auto
  img
    max-width: 100%
    height: auto
    display: block
    margin: 0 auto
    border: none
        
 /* Table */
 .parent
   width: 100%
   height: 100%
   display: table
   position: absolute
   top: 0
   left: 0
   .inner 
     display: table-cell
     text-align: center
     vertical-align: middle
.block
  display: inline-block
  img
    display: block
    border: none
      
/* Pseudo-element */
.parent 
  width: 100%
  height: 100%
  position: absolute
  top: 0
  left: 0
  overflow: auto
  white-space: nowrap
  text-align: center
  font-size: 0
  &:before
    height: 100%
    display: inline-block
    vertical-align: middle
    content: ''
.block
  display: inline-block
  white-space: normal
  vertical-align: middle
  text-align: left
  img
    display: block
    border: none
    
/* Flexbox */
.parent
  width: 100%
  height: 100%
  position: fixed
  top: 0
  left: 0
  display: flex
  align-items: center
  justify-content: center
  overflow: auto
.block
  background: #60a839
  img
    display: block
    border: none
    	
/* Button */
.parent
  width: 100%
  height: 100%
  position: absolute
  top: 0
  left: 0
  overflow: auto
  background: none
  border: none
  outline: none
.block
  display: inline-block
  img
    display: block
    border: none