Edit in JSFiddle

.ornek1{
width:100px;
height:100px;
background:#096;
}
.ornek1:hover{
transition:width 2s;
-webkit-transition:width 2s;
-moz-transition:width 2s;
width:300px;
} 

<div class="ornek1">css transition Özelliği öÖrnekler</div>