Vertical / horizontal alignment

  1. Negative margins
  2. Auto margins
  3. CSS calc()

Unknown width

  1. Lebedev method
  2. Inline-block + calc()

Unknown height

  1. Auto margins + display table

Unknown width & height

  1. Button
  2. 3-cols table
  3. Table-cell
  4. Inline-block with vertical-alignment by :before
  5. Transforms
  6. Flexboxes