.valid {
    border: 1px solid green;
    padding: 15px;
    background: #f0fff0;
}

.invalid {
    border: 1px solid red;
    padding: 15px;
    background: #fff0f0;
}
input#ldecv-id {
    width: 300px;
    letter-spacing: 4px;
}
 button#ldecv-btn {
        margin: 20px 0;
    }

@media(max-width:480px){

    button#ldecv-btn {
        width: 100%;
        margin: 20px 0;
    }
 
    input#ldecv-id {
    width: 100%;
    letter-spacing: 4px;
    text-align: center;
    }
}