This is more predictable then "line-height"
.loginBtn {_x000D_
background:url(images/loginBtn-center.jpg) repeat-x;_x000D_
width:175px;_x000D_
height:65px;_x000D_
margin:20px auto;_x000D_
border-radius:10px;_x000D_
-webkit-border-radius:10px;_x000D_
box-shadow:0 1px 2px #5e5d5b;_x000D_
}_x000D_
_x000D_
.loginBtn span {_x000D_
display: block;_x000D_
padding-top: 22px;_x000D_
text-align: center;_x000D_
line-height: 1em;_x000D_
}
_x000D_
<div id="loginBtn" class="loginBtn"><span>Log in</span></div>
_x000D_
.loginBtn {
display: flex;
align-items: center;
justify-content: center;
}