body {
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

#card-container {
    perspective: 1000px;
}

.card {
    position: relative;
    transform-style: preserve-3d;
    transition: transform 0.7s cubic-bezier(0.4, 0.2, 0.2, 1);
}

.card.flipped {
    transform: rotateY(180deg);
}

.card-face {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    -webkit-backface-visibility: hidden;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 1.5rem;
}

.card-back {
    transform: rotateY(180deg);
}

.favorite-btn {
    background: none;
    border: none;
    cursor: pointer;
    padding: 0;
}

.favorite-btn.is-favorite {
    color: #FFD700;
}

.missed-word-item .mistake-count {
    color: #dc3545;
    font-weight: bold;
    margin-left: 10px;
}

#performance-message {
    font-size: 1.5em;
    font-weight: bold;
    margin-top: 20px;
    padding: 15px;
    border-radius: 5px;
}

.msg-perfect { color: #15803d; background-color: #dcfce7; }
.msg-good { color: #1d4ed8; background-color: #dbeafe; }
.msg-average { color: #d97706; background-color: #fefce8; }
.msg-poor { color: #be123c; background-color: #ffe4e6; }