Elements properties may be transitioned from one value to another as they have recognizable values in-between one another using:  transition-property, transition-duration, transition-timing-function   and transition-delay. Transition effects can be applied to a wide variety of CSS properties, including:

• background-color
• background-position
• border-color
• border-width
• border-spacing
• bottom
• color
• crop
• font-size
• font-weight
• height
• letter-spacing
• line-height
• margin
• opacity
• outline-color
• padding
• text-indent
• text-shadow
• vertical-align
• visibility
• width
• word-spacing
• z-index ... and more

EXAMPLES OF CSS TRANSITIONS ON HOVER WITH CODES
where you can copy, analyze and use codes
https://bootstrapbay.com/blog/css-transitions-buttons/
http://www.webdesignerdepot.com/2014/05/8-simple-css3-transitions-that-will-wow-your-users/
http://fivera.net/simple-cool-live-examples-image-hover-css-effect/
http://designshack.net/?p=19746
http://designshack.net/articles/css/joshuajohnson-2/
http://codepen.io/nxworld/pen/ZYNOBZ 
http://www.webdesignerdepot.com/2015/02/3-cool-css3-image-hover-effects/