Reveal Icon Button - Bootstrap 3 - css

Question

How to create a reveal icon inside button on hover in TB3. I tried to mimic this behavior using CSS transitions and position property. But I essentially need is to have a separate background color for icon and button. Here is what I am doing right now.
HTML Markup
<button class="btn btn-dark icon-revealed">
<span class="glyphicon glyphicon-cloud-download"></span>
Download
</button>
CSS Code
.btn.icon-revealed > span {
left: -30px;
width: 0;
-webkit-transition: all .5s ease-in-out;
-moz-transition: all .5s ease-in-out;
-o-transition: all .5s ease-in-out;
-ms-transition: all .5s ease-in-out;
}
.btn.icon-revealed:hover > span {
width: 20%;
-webkit-transform: translate(2em,0);
-moz-transform: translate(2em,0);
-o-transform: translate(2em,0);
-ms-transform: translate(2em,0);
}
What I want to Achieve
Notice the background color of icon and button changed on hover state. I could not able to do that. How can I achieve this in TB3?

Answer 1

Here's an alternative way that smooths out the transition.
.btn-dark {
border: none;
font-family: inherit;
font-size: inherit;
color: #fff;
background: none;
padding: 15px 30px;
display: inline-block;
text-transform: uppercase;
letter-spacing: 1px;
font-weight: 500;
outline: none;
position: relative;
-webkit-transition: all 0.3s;
-moz-transition: all 0.3s;
transition: all 0.3s;
}
.btn-dark:after {
content: '';
position: absolute;
z-index: -1;
-webkit-transition: all 0.3s;
-moz-transition: all 0.3s;
transition: all 0.3s;
}
.btn-icon {
background: #4E7878;
color: #fff;
line-height: 20px;
font-size: 14px;
overflow: hidden;
-webkit-backface-visibility: hidden;
-moz-backface-visibility: hidden;
backface-visibility: hidden;
}
.btn-icon span {
display: inline-block;
width: 100%;
height: 100%;
-webkit-transition: all 0.3s;
-webkit-backface-visibility: hidden;
-moz-transition: all 0.3s;
-moz-backface-visibility: hidden;
transition: all 0.3s;
backface-visibility: hidden;
}
.btn-icon:before {
background: #4A6B6B;
position: absolute;
height: 100%;
width: 30%;
line-height: 2.5;
font-size: 150%;
-webkit-transition: all 0.3s;
-moz-transition: all 0.3s;
transition: all 0.3s;
}
.btn-download:hover span {
-webkit-transform: translateX(25%);
-moz-transform: translateX(25%);
-ms-transform: translateX(25%);
transform: translateX(25%);
color: #fff;
}
.btn-download:before {
left: -100%;
top: 0;
}
.btn-download:hover:before {
left: 0%;
}
.icon-reveal:before {
content: "\e197";
font-family: 'Glyphicons Halflings';
color: #fff;
}
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css" rel="stylesheet" />
<hr>
<div class="container">
<button class="btn-dark btn-icon btn-download icon-reveal"><span> Download</span>
</button>
</div>

Answer 2

You can create that effect using multiple backgrounds with linear-gradient. Code explanantion in comments
.btn.icon-revealed {
margin: 10px; /* Added for SO snippet, not required */
width: 115px; /* Added fixed width for avoiding jump */
}
.btn.icon-revealed > span {
left: -40px;
width: 0;
-webkit-transition: all .5s ease-in-out;
-moz-transition: all .5s ease-in-out;
-o-transition: all .5s ease-in-out;
-ms-transition: all .5s ease-in-out;
}
.btn.icon-revealed:hover > span {
width: 20%;
-webkit-transform: translate(2.5em, 0);
-moz-transform: translate(2.5em, 0);
-o-transform: translate(2.5em, 0);
-ms-transform: translate(2.5em, 0);
}
/* Added code */
.btn.icon-revealed {
background: #53777A;
color: #fff;
}
.btn.icon-revealed:hover {
background: linear-gradient(to right, #4B6B6E 0%, #4B6B6E 30%, #53777A 30%);
/* Start color---^, End at 30%-^, ^-- Start second color */
color: #fff;
}
.btn.icon-revealed:hover .text {
padding-left: 5px;
}
<link href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.5/css/bootstrap.min.css" rel="stylesheet" />
<button class="btn btn-dark icon-revealed">
<span class="glyphicon glyphicon-cloud-download"></span>
<span class="text">Download</span>
</button>