Ross Alex

<label class="btn"><input type="checkbox" class="cht" /><span></span>Sign up</label>

.btn {
    overflow:hidden;
    position:relative;
}
.btn input {
    visibility: hidden;
    position:absolute;
    left:-100%;
}
.btn span {
    display:inline-block;
    position: relative;
    width:32px;
    height:32px;
    border: 1px solid red;
    margin-right:8px;
}
.btn span:before {
    content:"";
    transition: all 0.25s ease;
    opacity:0;
    position: absolute;
    background-color: red;
    width:16px;
    height:16px;
    left: 8px;
    top:8px;
}
.btn input:checked + span:before {opacity:1;}