index.css

* {
    margin: 0px auto;
    padding: 0px;
    text-align: center;
    font-family: 'Lato', sans-serif;
}

.cotn_principal {
    position: absolute;
    width: 100%;
    height: 100%;
    /* Permalink - use to edit and share this gradient: http://colorzilla.com/gradient-editor/#cfd8dc+0,607d8b+100,b0bec5+100 */
    background: #aac4bc;
    /* Old browsers */
    background: -moz-linear-gradient(-45deg, #aac4bc 0%, #eca8a8 100%, #eed5a9 100%);
    /* FF3.6-15 */
    background: -webkit-linear-gradient(-45deg, #aac4bc 0%, #eca8a8 100%, #eed5a9 100%);
    /* Chrome10-25,Safari5.1-6 */
    background: linear-gradient(135deg, #aac4bc 0%, #eca8a8 100%, #eed5a9 100%);
    /* W3C, IE10+, FF16+, Chrome26+, Opera12+, Safari7+ */
    filter: progid: DXImageTransform.Microsoft.gradient( startColorstr='#cfd8dc', endColorstr='#b0bec5', GradientType=1);
    /* IE6-9 fallback on horizontal gradient */
}

.cont_centrar {
    position: relative;
    float: left;
    width: 100%;
}

.cont_login {
    position: relative;
    width: 640px;
    left: 50%;
    margin-left: -320px;
}

.cont_back_info {
    position: relative;
    float: left;
    width: 640px;
    height: 280px;
    overflow: hidden;
    background-color: #fff;
    margin-top: 100px;
    box-shadow: 1px 10px 30px -10px rgba(0, 0, 0, 0.5);
}

.cont_forms {
    position: absolute;
    overflow: hidden;
    top: 100px;
    left: 0px;
    width: 320px;
    height: 280px;
    background-color: #eee;
    -webkit-transition: all 0.5s;
    -moz-transition: all 0.5s;
    -ms-transition: all 0.5s;
    -o-transition: all 0.5s;
    transition: all 0.5s;
}

.cont_forms_active_login {
    box-shadow: 1px 10px 30px -10px rgba(0, 0, 0, 0.5);
    height: 420px;
    top: 20px;
    left: 0px;
    -webkit-transition: all 0.5s;
    -moz-transition: all 0.5s;
    -ms-transition: all 0.5s;
    -o-transition: all 0.5s;
    transition: all 0.5s;
}

.cont_forms_active_sign_up {
    box-shadow: 1px 10px 30px -10px rgba(0, 0, 0, 0.5);
    height: 420px;
    top: 20px;
    left: 320px;
    -webkit-transition: all 0.5s;
    -moz-transition: all 0.5s;
    -ms-transition: all 0.5s;
    -o-transition: all 0.5s;
    transition: all 0.5s;
}

.cont_img_back_grey {
    position: absolute;
    width: 950px;
    top: -80px;
    left: -116px;
}

.cont_img_back_grey > img {
    width: 100%;
    -webkit-filter: grayscale(100%);
    filter: grayscale(100%);
    opacity: 0.2;
    animation-name: animar_fondo;
    animation-duration: 20s;
    animation-timing-function: linear;
    animation-iteration-count: infinite;
    animation-direction: alternate;
}

.cont_img_back_ {
    position: absolute;
    width: 950px;
    top: -80px;
    left: -116px;
}

.cont_img_back_ > img {
    width: 100%;
    opacity: 0.3;
    animation-name: animar_fondo;
    animation-duration: 20s;
    animation-timing-function: linear;
    animation-iteration-count: infinite;
    animation-direction: alternate;
}

.cont_forms_active_login > .cont_img_back_ {
    top: 0px;
    -webkit-transition: all 0.5s;
    -moz-transition: all 0.5s;
    -ms-transition: all 0.5s;
    -o-transition: all 0.5s;
    transition: all 0.5s;
}

.cont_forms_active_sign_up > .cont_img_back_ {
    top: 0px;
    left: -435px;
    -webkit-transition: all 0.5s;
    -moz-transition: all 0.5s;
    -ms-transition: all 0.5s;
    -o-transition: all 0.5s;
    transition: all 0.5s;
}

.cont_info_log_sign_up {
    position: absolute;
    width: 640px;
    height: 280px;
    top: 100px;
    z-index: 1;
}

.col_md_login {
    position: relative;
    float: left;
    width: 50%;
}

.col_md_login > h2 {
    font-weight: 400;
    margin-top: 70px;
    color: #757575;
}

.col_md_login > p {
    font-weight: 400;
    margin-top: 15px;
    width: 80%;
    color: #37474F;
}

.btn_login {
    background-color: #FF9800;
    border: none;
    padding: 10px;
    width: 200px;
    border-radius: 3px;
    box-shadow: 1px 5px 20px -5px rgba(0, 0, 0, 0.4);
    color: #fff;
    margin-top: 10px;
    cursor: pointer;
}

.col_md_sign_up {
    position: relative;
    float: left;
    width: 50%;
}

.cont_ba_opcitiy > h2 {
    font-weight: 400;
    color: #fff;
}

.cont_ba_opcitiy > p {
    font-weight: 400;
    margin-top: 15px;
    color: #fff;
}


/* ----------------------------------
background text    
------------------------------------
 */

.cont_ba_opcitiy {
    position: relative;
    background-color: rgba(187, 168, 170, 0.79);
    width: 80%;
    border-radius: 3px;
    margin-top: 60px;
    padding: 15px 0px;
}

.btn_sign_up {
    background-color: #f44336;
    border: none;
    padding: 10px;
    width: 200px;
    border-radius: 3px;
    box-shadow: 1px 5px 20px -5px rgba(0, 0, 0, 0.4);
    color: #fff;
    margin-top: 10px;
    cursor: pointer;
}

.cont_forms_active_sign_up {
    z-index: 2;
}

@-webkit-keyframes animar_fondo {
    from {
        -webkit-transform: scale(1) translate(0px);
        -moz-transform: scale(1) translate(0px);
        -ms-transform: scale(1) translate(0px);
        -o-transform: scale(1) translate(0px);
        transform: scale(1) translate(0px);
    }
    to {
        -webkit-transform: scale(1.5) translate(50px);
        -moz-transform: scale(1.5) translate(50px);
        -ms-transform: scale(1.5) translate(50px);
        -o-transform: scale(1.5) translate(50px);
        transform: scale(1.5) translate(50px);
    }
}

@-o-keyframes identifier {
    from {
        -webkit-transform: scale(1);
        -moz-transform: scale(1);
        -ms-transform: scale(1);
        -o-transform: scale(1);
        transform: scale(1);
    }
    to {
        -webkit-transform: scale(1.5);
        -moz-transform: scale(1.5);
        -ms-transform: scale(1.5);
        -o-transform: scale(1.5);
        transform: scale(1.5);
    }
}

@-moz-keyframes identifier {
    from {
        -webkit-transform: scale(1);
        -moz-transform: scale(1);
        -ms-transform: scale(1);
        -o-transform: scale(1);
        transform: scale(1);
    }
    to {
        -webkit-transform: scale(1.5);
        -moz-transform: scale(1.5);
        -ms-transform: scale(1.5);
        -o-transform: scale(1.5);
        transform: scale(1.5);
    }
}

@keyframes identifier {
    from {
        -webkit-transform: scale(1);
        -moz-transform: scale(1);
        -ms-transform: scale(1);
        -o-transform: scale(1);
        transform: scale(1);
    }
    to {
        -webkit-transform: scale(1.5);
        -moz-transform: scale(1.5);
        -ms-transform: scale(1.5);
        -o-transform: scale(1.5);
        transform: scale(1.5);
    }
}

.cont_form_login {
    position: absolute;
    opacity: 0;
    display: none;
    width: 320px;
    -webkit-transition: all 0.5s;
    -moz-transition: all 0.5s;
    -ms-transition: all 0.5s;
    -o-transition: all 0.5s;
    transition: all 0.5s;
}

.cont_forms_active_login {
    z-index: 2;
}

.cont_forms_active_login >.cont_form_login {}

.cont_form_sign_up {
    position: absolute;
    width: 320px;
    float: left;
    opacity: 0;
    display: none;
    -webkit-transition: all 0.5s;
    -moz-transition: all 0.5s;
    -ms-transition: all 0.5s;
    -o-transition: all 0.5s;
    transition: all 0.5s;
}

.cont_form_sign_up > input {
    text-align: left;
    padding: 15px 5px;
    margin-left: 10px;
    margin-top: 20px;
    width: 260px;
    border: none;
    color: #757575;
}

.cont_form_sign_up > h2 {
    margin-top: 50px;
    font-weight: 400;
    color: #757575;
}

.cont_form_login > input {
    padding: 15px 5px;
    margin-left: 10px;
    margin-top: 20px;
    width: 260px;
    border: none;
    text-align: left;
    color: #757575;
}

.cont_form_login > h2 {
    margin-top: 110px;
    font-weight: 400;
    color: #757575;
}

.cont_form_login > a,
.cont_form_sign_up > a {
    color: #757575;
    position: relative;
    float: left;
    margin: 10px;
    margin-left: 30px;
}