style.css

@import url('https://fonts.googleapis.com/css2?family=Space+Grotesk:wght@500&display=swap');

*{
    margin: 0;padding: 0; box-sizing: border-box;
}

body{
    font-family: 'Space Grotesk', sans-serif;
    display: flex;
    flex-direction: column;
}
main{
    display: flex;
}

.leftSection{
    background: url(./images/bg-main-desktop.png);
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
    height: 100vh;
    width: 35vw;
    color: white;
}
.cards{
    display: flex;
    flex-direction: column;
    /* align-items: flex-end; */
    justify-content: space-evenly;
    margin-left: 40%;
    height: 100vh;
}

.cardFront{
    background: url(./images/bg-card-front.png);
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
    height: 35vh;
    width: 65vh;
    padding: 20px;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    cursor: pointer;
}
.nameSection{
    display: flex;
    justify-content: space-between;
}
.cardFront h2{
    text-align: center;
    letter-spacing: 5px;
}
.cardBack{
    background: url(./images/bg-card-back.png);
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
    height: 35vh;
    width: 65vh;
    margin-left: 25%;
    padding: 40px;
    cursor: pointer;
    display: flex;
    justify-content: flex-end;
    align-items: center;
}
.cardBack h3{
    letter-spacing: 2px;
    margin-bottom: 5px;
}
.error{
    color: red;
    font-style: italic;
}

.rightSection{
    display: flex;
    flex-direction: column;
    width: 60vw;
    align-items:center;
    justify-content: center;
    margin-left: 15%;
}

.nameinput,.numberinput,.expDateinput,.cvcInput{
    display: flex;
    flex-direction: column;
    width: 70%;
}
.bottomData{
    display: flex;
    width: 70%;
    align-items: center;
}
label{
    font-size: 12px;
    letter-spacing: 3px;
    margin-top: 10px;
    margin-bottom: 10px;
    color:  hsl(278, 68%, 11%);
    text-transform: uppercase;
}
::placeholder{
    font-family: 'Space Grotesk', sans-serif;
    font-weight: 500;
    letter-spacing: 3px;
    color: hsl(279, 6%, 55%);
}
input{
    font-family:'Space Grotesk', sans-serif;
    color: hsl(278, 68%, 11%);
    padding: 10px;
    font-size: 16px;
    border-radius: 10px;
    border: 1px solid hsl(279, 6%, 55%);
    
}
input:hover{
    border: none;
    outline: 2px solid hsl(278, 68%, 11%);
}
.eNum{
    width: 30%;
    margin-right: 20px;
    text-align: center;
}
button{
    font-family: 'Space Grotesk', sans-serif;
    width: 70%;
    margin-top: 20px;
    padding: 10px;
    border-radius: 10px;
    font-size: 16px;
    background-color: hsl(278, 68%, 11%);
    color: white;
}
.AfterSection{
    display: none;
}
.thanks{
    width: 100%;
    display: flex;
    flex-direction: column;
    align-items: center;
}
.thanks img{
    width: 30%;
}
h1{
    display: block;
}
.thanks button{
    width: 100%;
}

footer{
    margin-top: 10px;
    margin-bottom: 10px;
}
footer a{
    text-decoration: none;
    color: white;
    padding: 2px;
    background-color: hsl(278, 68%, 11%);
}

/* responsive */

@media (max-width:408px) {
    main{
        display: flex;
        flex-direction: column;
    }
    .leftSection{
        width: 100vw;
        height: 45vh;
    }
    .cards{
        margin: 20px;
        align-items: center;
        justify-content: flex-start;
        margin-top: 40%;
    }
    .cardFront, .cardBack{
        border-radius: 10px;
        width: 85vw;
        height: 35vh;
        font-size: 13px;
    }
    .cardFront{
        margin-left: -10%;
        z-index: 1;
    }
    .cardBack{
        margin-left: 5%;
        margin-top: -105%;
        z-index: 0;
    }
    .cardFront h2{
        font-size: 12px;
    }

    .rightSection{
        margin-left: 0%;
        width: 100vw;
        margin-top: 30%;
    }
    .nameinput,.numberinput{
        display: flex;
        flex-direction: column;
        width: 85%;
    }
    .bottomData{
        display: flex;
        width: 85%;
        align-items: center;
    }
    .bottomData label{
        font-size: 13px;
        letter-spacing: 0px;
    }
    .expDateinput, .cvcInput{
        width: 50%;
    }
    .eNum{
        width: 40%;
        margin-right: 10px;
        text-align: center;
    }
    ::placeholder{
        font-size: 14px;
    }
    button{
        width: 85% ;
    }
    .error{
        font-size: 14px;
    }
    footer{
        text-align: center;
        font-size: 14px;
    }
}