header {
     border-style: solid;
     border-top-width: 5px;
     background-color: red;
     display: flex;
     align-items: center;
     justify-content: space-between;
}
 .abstract p {
     background-color: yellow;
}
 .understated {
    font-size: small;
}
 header .header-button {
     margin: 0 10px;
}
 header h1 {
     margin-right: auto;
}

.two-columns {
   width:700px;
   margin:0px 0px;
}
.left-column {
   float:left;
   width:300px;
   background-color: antiquewhite;
}
.right-column {
   float:right;
   width:400px;
}

 * {
     margin: 0px auto;
     padding: 0px;
     text-align: center;
     font-family: 'Open Sans', 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: #cfd8dc;
    /* Old browsers */
     background: -moz-linear-gradient(-45deg, #cfd8dc 0%, #607d8b 100%, #b0bec5 100%);
    /* FF3.6-15 */
     background: -webkit-linear-gradient(-45deg, #cfd8dc 0%,#607d8b 100%,#b0bec5 100%);
    /* Chrome10-25,Safari5.1-6 */
     background: linear-gradient(135deg, #cfd8dc 0%,#607d8b 100%,#b0bec5 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: 0px;
     margin-left: 50px;
}
 .cont_back_info {
     position: relative;
     float: left;
     width: 640px;
     height: 350px;
     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: 350px;
     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: 620px;
     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: #26C6DA;
     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(120, 144, 156, 0.55);
     width: 80%;
     border-radius:3px ;
     margin-top: 60px;
     padding: 15px 0px;
}
 .btn_sign_up {
     background-color: #ef5350;
     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;
}