Change Google Material Icon to hover only with html / css

Question

I want to change Google Material Icon(actual icon) to a hover button. I would like to do this only with HTMLand CSS. I would like it to go from the plus sign to something like the check sign, in particular using the done icon. Codeden is below. thank

.material-icons.md1 {
    font-family: 'Material Icons';
    font-weight: normal;
    font-style: normal;
    font-size: 33px;
    margin-top: 12px;
}
.btnwrap {
    position: fixed;
    z-index: 2;
    height: 60px;
    width: 300px;
    background-color: #074fb2;
    font-size: 20px;
    display: block;
    text-align: center;
    vertical-align: middle;
    line-height: 60px;
    color: #fff;
    border-radius: 50px;
    cursor: pointer;
}
.btntext1 {
    position: absolute;
    left:85px; 
    transition: all .1s;
}
.btntext2 {
    position: absolute;
    width: 100%;
    transition: all .2s;
    opacity: 0;
}
.innerbtn {
    z-index: 1;
    position: relative;
    float: left;
    height: 56px;
    width: 56px;
    background-color: #3e81dc;
    border-radius: 50px;
    display: inline-block;
    margin-top: 2px;
    margin-left:2px; 
    transition: all 1s;
}
.btnwrap:hover .btntext1 {
    opacity: 0;
    transition: all .5s;
}
.btnwrap:hover .btntext2 {
    opacity: 1;
    transition: all .5s;
}
.btnwrap:hover .innerbtn {
    margin-left: 242px;
}
<link href="https://fonts.googleapis.com/icon?family=Material+Icons"
  rel="stylesheet">
<div id="button1" class="btnwrap" title="download_btn">
<div class="innerbtn"><i class="material-icons md1">add</i></div> 
<div class="btntext2">Click Now</div>
<div class="btntext1">Download for FREE</div>
</div>

https://codepen.io/anon/pen/YYEXYy

Answer 1

So, I will answer my own question here. Leave the html blank, add "content" with ": before" in the CSS, and then change this to ": before" with the hang state. see branched Codepen:

<i class="material-icons md1" style="margin-top: 12px;"></i></div> 

.material-icons.md1::before{
    font-family: 'Material Icons';
    font-weight: normal;
    font-style: normal;
    font-size: 33px;
    content:"add"; 
}

.btnwrap:hover .material-icons.md1::before{
    content:"done"; 
}

https://codepen.io/anon/pen/aEVOEr

Answer 2

HTML

<i class="material-icons md1"></i>

CSS

.material-icons.md1::before{
    content:"add"; 
}

.material-icons.md1:hover::before{
    content:"remove"; 
}

https://codepen.io/Funny0Frank/pen/RMYBvQ