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

body {
    width: 100vw;
    height: 100vh;
    overflow: hidden;
    position: relative;
}

.background {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
    z-index: 0;
}

.container {
    position: relative;
    width: 100%;
    height: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 1;
}

.envelope {
    max-width: 40%;
    max-height: 40%;
    cursor: pointer;
    transition: transform 0.3s ease;
}

.envelope.small {
    max-width: 24%;
    max-height: 24%;
}

.envelope.medium {
    max-width: 28%;
    max-height: 28%;
}

.envelope:hover {
    transform: scale(1.05);
}

.letter {
    max-width: 64%;
    max-height: 64%;
    cursor: pointer;
    animation: fadeIn 0.5s ease-in;
    transition: transform 0.3s ease;
}

.letter:hover {
    transform: scale(1.02);
}

.hidden {
    display: none;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: scale(0.9);
    }
    to {
        opacity: 1;
        transform: scale(1);
    }
}
@media (max-width: 768px) {
    img {
      max-width: 90vw; /* 모바일 전체 너비의 90% */
    }
  }