style.css

body {
    margin: 0px;
    padding: 0px;
    background: #F3F5FC;
    font-family: 'Trebuchet MS', 'Lucida Sans Unicode', 'Lucida Grande', 'Lucida Sans', Arial, sans-serif;
}

.container {
    margin: auto;
    width: 960px;
    height: 600px;
    padding: 5px;    
}
.logo {
    width: 100%;
    float: left;
}
.left{
    float: left;
    width: 70%;
    height: 70%;
    border-radius: 24px;
   
    
}
.right{
    float: right;
    width: 30%;
    height: auto;
    border-radius: 24px;
    background: white ;
}
.text-input{
    font-family: 'Trebuchet MS', 'Lucida Sans Unicode', 'Lucida Grande', 'Lucida Sans', Arial, sans-serif;    
}
.left-button{
    float: left;
    width: 70%;
    height: auto;
    border-radius: 24px;    
}
.encriptar-button {
    color: #F3F5FC;
    font-family: 'Trebuchet MS', 'Lucida Sans Unicode', 'Lucida Grande', 'Lucida Sans', Arial, sans-serif;    
}
.desencriptar-button {
    font-family: 'Trebuchet MS', 'Lucida Sans Unicode', 'Lucida Grande', 'Lucida Sans', Arial, sans-serif;    
}
.logoImg{
    margin-top: 1%;
    margin-left: 5%;
    float: inherit;
}
.tittle{
    float: inherit;
    margin-left: 20%;
}
.text-input{
    float: left;
    margin-left: 10%;
    margin-top: 10%;
    width: 80%;
    height: 80%;
    color: #0A3871;
    font-size: 20px;
    border: none;
    outline: none;
    background: #F3F5FC;
}
#imgDer{
    margin-left: 2%;
    margin-top: 20%;
    width: 90%;
    height: auto;
}
#texto{
    margin-left: 7%;
    margin-right: 5%;
}
#texto2{
    float: left;
    margin-left: 10%;
    color:#0A3871;
    width: 80%;
    height: 60%;
    border: none;
    outline: none;
    font-size: 15px;  
}
#btn-encriptar{
    padding: 24px;
    width: 30%;
    height: 60%;
    border-radius: 24px;
    margin-left: 15%;
    background:#0A3871 ;
}
#btn-desencriptar{
    padding: 24px;
    width: 30%;
    height: 60%;
    border-radius: 24px;
    margin-left: 10%;
    background:#D8DFE8 ;
}
#copiar{
    margin-left: 33%;
    margin-top: 90%;
    padding: 24px;
    width: 40%;
    height: 10%;
    background:#D8DFE8 ;
    border-radius: 24px ;
    display: none;
}

@media (max-width:768px){
    .container{
        flex-direction: column;
        align-items: center;
        align-items: stretch;

}