:root {
    --primary-color: #4a90e2;
    --secondary-color: #50e3c2;
    --background-color: #f4f6f9;
    --card-bg: #ffffff;
    --text-color: #333333;
    --text-light: #777777;
    --success-color: #2ecc71;
    --danger-color: #e74c3c;
    --shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
    --radius: 16px;
    --font-family: 'Inter', sans-serif;
}

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

body {
    font-family: var(--font-family);
    background-color: var(--background-color);
    color: var(--text-color);
    display: flex;
    flex-direction: column;
    min-height: 100vh;
    align-items: center;
    padding: 20px;
}

header {
    width: 100%;
    max-width: 600px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 30px;
}

h1 {
    font-size: 1.8rem;
    font-weight: 700;
    color: var(--primary-color);
    display: flex;
    align-items: center;
    gap: 10px;
}

.flag-icon {
    font-size: 1.5rem;
}

/* Stats Container */
.stats-container {
    display: flex;
    justify-content: space-around;
    width: 100%;
    max-width: 600px;
    background: var(--card-bg);
    padding: 15px;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    margin-bottom: 30px;
}

.stat-item {
    text-align: center;
}

.stat-value {
    font-size: 1.2rem;
    font-weight: bold;
    color: var(--primary-color);
}

.stat-label {
    font-size: 0.8rem;
    color: var(--text-light);
}

/* Card Container */
.card-container {
    perspective: 1000px;
    width: 100%;
    max-width: 400px;
    height: 300px;
    margin-bottom: 30px;
    cursor: pointer;
}

.flashcard {
    position: relative;
    width: 100%;
    height: 100%;
    text-align: center;
    transition: transform 0.8s;
    transform-style: preserve-3d;
    box-shadow: var(--shadow);
    border-radius: var(--radius);
}

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

.card-face {
    position: absolute;
    width: 100%;
    height: 100%;
    -webkit-backface-visibility: hidden;
    backface-visibility: hidden;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    background-color: var(--card-bg);
    border-radius: var(--radius);
    padding: 20px;
}

.card-face.front {
    color: var(--text-color);
}

.card-face.back {
    background-color: var(--primary-color);
    color: white;
    transform: rotateY(180deg);
}

.word {
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: 15px;
}

.pronunciation-btn {
    background: none;
    border: none;
    cursor: pointer;
    font-size: 1.5rem;
    color: var(--secondary-color);
    transition: transform 0.2s;
}

.pronunciation-btn:hover {
    transform: scale(1.1);
}

/* Controls */
.controls {
    display: flex;
    gap: 20px;
    margin-bottom: 30px;
}

.btn {
    padding: 12px 24px;
    border: none;
    border-radius: 50px;
    font-size: 1rem;
    cursor: pointer;
    font-weight: 600;
    transition: transform 0.2s, box-shadow 0.2s;
    display: flex;
    align-items: center;
    gap: 8px;
}

.btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 5px 15px rgba(0,0,0,0.1);
}

.btn-know {
    background-color: var(--success-color);
    color: white;
}

.btn-dont-know {
    background-color: var(--danger-color);
    color: white;
}

/* Add Form */
.add-form-container {
    width: 100%;
    max-width: 600px;
    background: var(--card-bg);
    padding: 20px;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
}

.add-form-container h2 {
    font-size: 1.2rem;
    margin-bottom: 15px;
    color: var(--text-color);
}

.form-group {
    margin-bottom: 15px;
}

input, select {
    width: 100%;
    padding: 10px;
    border: 1px solid #ddd;
    border-radius: 8px;
    font-family: inherit;
    font-size: 1rem;
}

.btn-submit {
    width: 100%;
    background-color: var(--primary-color);
    color: white;
}

/* Responsive */
@media (max-width: 480px) {
    .word {
        font-size: 2rem;
    }
    .card-container {
        height: 250px;
    }
    .controls {
        flex-direction: column;
        width: 100%;
    }
    .btn {
        width: 100%;
        justify-content: center;
    }
}