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

body {
    min-height: 100vh;
    font-family: Arial, sans-serif;

    display: flex;
    justify-content: center;
    align-items: center;

    background: linear-gradient(
        135deg,
        #ff9a9e,
        #fad0c4,
        #fbc2eb,
        #a6c1ee
    );

    overflow: hidden;
}

/* Khung sinh nhật */

.birthday-card {
    width: 90%;
    max-width: 650px;

    padding: 45px 30px;

    text-align: center;

    background: rgba(255, 255, 255, 0.9);

    border-radius: 30px;

    box-shadow:
        0 20px 50px rgba(0, 0, 0, 0.2);

    position: relative;
    z-index: 5;

    animation: appear 1.2s ease;
}

/* Bánh sinh nhật */

.cake {
    font-size: 75px;

    animation: bounce 2s infinite;
}

.small-title {
    margin-top: 10px;

    font-size: 18px;
    font-weight: bold;

    letter-spacing: 4px;

    color: #ff4f81;
}

h1 {
    margin-top: 15px;

    font-size: 42px;

    color: #e91e63;

    text-shadow:
        2px 2px 0 #ffd1df;
}

.line {
    width: 100px;
    height: 4px;

    margin: 18px auto;

    border-radius: 10px;

    background: #ff6b9a;
}

.message {
    font-size: 23px;

    color: #444;

    margin-bottom: 15px;
}

.wish {
    max-width: 520px;

    margin: auto;

    line-height: 1.8;

    font-size: 17px;

    color: #666;
}

/* Hộp quà */

.gift {
    font-size: 65px;

    margin: 25px 0;

    animation: shake 1.5s infinite;
}

/* Button */

button {
    border: none;

    padding: 15px 30px;

    border-radius: 50px;

    background: linear-gradient(
        45deg,
        #ff4f81,
        #ff85a2
    );

    color: white;

    font-size: 17px;

    font-weight: bold;

    cursor: pointer;

    box-shadow:
        0 8px 20px rgba(255, 79, 129, 0.35);

    transition: 0.3s;
}

button:hover {
    transform: scale(1.08);

    box-shadow:
        0 12px 25px rgba(255, 79, 129, 0.5);
}

/* Lời chúc đặc biệt */

#special-message {
    margin-top: 25px;

    color: #e91e63;

    font-size: 18px;

    font-weight: bold;

    line-height: 1.7;

    animation: fadeIn 1s ease;
}

/* Footer */

.footer {
    margin-top: 30px;

    font-size: 13px;

    color: #999;
}

/* Bóng bay */

.balloon {
    position: fixed;

    font-size: 70px;

    z-index: 1;

    animation: float 5s ease-in-out infinite;
}

.balloon1 {
    left: 5%;
    top: 10%;
}

.balloon2 {
    right: 7%;
    top: 15%;

    animation-delay: 1s;
}

.balloon3 {
    left: 10%;
    bottom: 8%;

    animation-delay: 2s;
}

.balloon4 {
    right: 10%;
    bottom: 10%;

    animation-delay: 3s;
}

/* Trái tim bay */

.heart {
    position: fixed;

    bottom: -50px;

    font-size: 25px;

    animation: heartFly linear forwards;

    z-index: 10;
}

/* Animation */

@keyframes appear {
    from {
        opacity: 0;
        transform: scale(0.7) translateY(50px);
    }

    to {
        opacity: 1;
        transform: scale(1) translateY(0);
    }
}

@keyframes bounce {
0%, 100% {
        transform: translateY(0);
    }

    50% {
        transform: translateY(-12px);
    }
}

@keyframes shake {
    0%, 100% {
        transform: rotate(0);
    }

    25% {
        transform: rotate(-8deg);
    }

    75% {
        transform: rotate(8deg);
    }
}

@keyframes float {
    0%, 100% {
        transform: translateY(0) rotate(-5deg);
    }

    50% {
        transform: translateY(-30px) rotate(5deg);
    }
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes heartFly {
    from {
        bottom: -50px;
        opacity: 1;
        transform: translateX(0) rotate(0);
    }

    to {
        bottom: 110vh;
        opacity: 0;
        transform: translateX(100px) rotate(360deg);
    }
}

/* Responsive điện thoại */

@media (max-width: 600px) {

    .birthday-card {
        padding: 35px 20px;
    }

    .cake {
        font-size: 60px;
    }

    h1 {
        font-size: 30px;
    }

    .small-title {
        font-size: 14px;
        letter-spacing: 2px;
    }

    .message {
        font-size: 19px;
    }

    .wish {
        font-size: 15px;
    }

    .balloon {
        font-size: 45px;
    }

    .gift {
        font-size: 50px;
    }
}