:root {
    --primary: #3498db;
    --primary-dark: #2980b9;
    --success: #2ecc71;
    --danger: #e74c3c;
    --text-main: #2c3e50;
    --text-sub: #7f8c8d;
    --bg-body: #f8fafd;
    --card-bg: #ffffff;
    --border: #e0e0e0;
    --shadow-sm: 0 2px 5px rgba(0,0,0,0.05);
    --shadow-md: 0 10px 30px rgba(0,0,0,0.08);
}

body.dark-mode {
    --bg-body: #1a1a2e;
    --card-bg: #16213e;
    --text-main: #e9ecef;
    --text-sub: #a2a8d3;
    --border: #2a3255;
    --shadow-md: 0 10px 30px rgba(0,0,0,0.4);
}

body {
    background-color: var(--bg-body); color: var(--text-main);
    font-family: 'Inter', sans-serif; margin: 0;
    transition: background 0.3s ease, color 0.3s ease;
}

/* --- Header --- */
header {
    display: flex; justify-content: space-between; align-items: center;
    padding: 15px 5%; background: var(--card-bg);
    box-shadow: var(--shadow-sm); position: sticky; top: 0; z-index: 100;
}

.logo-area { display: flex; align-items: center; gap: 12px; }

.logo-box {
    background: var(--primary); color: white;
    width: 40px; height: 40px;
    border-radius: 10px;
    display: flex; align-items: center; justify-content: center;
    font-size: 1.2rem;
}

.brand h1 { font-size: 1.3rem; font-weight: 700; margin: 0; }
.brand p { font-size: 0.85rem; margin: 2px 0 0 0; color: var(--text-sub); }

.header-actions { display: flex; gap: 12px; align-items: center; }

/* Theme Toggle - Smaller Size as requested */
.icon-btn.rounded-square {
    background: transparent; border: 1px solid var(--border);
    color: var(--text-sub); width: 34px; height: 34px; 
    border-radius: 8px; cursor: pointer; transition: all 0.2s;
    display: flex; align-items: center; justify-content: center;
    font-size: 0.9rem;
}
.icon-btn.rounded-square:hover {
    background: rgba(52, 152, 219, 0.05); border-color: var(--primary); color: var(--primary);
}

.add-btn {
    background: var(--primary); color: white; border: none;
    padding: 9px 20px; border-radius: 8px; font-weight: 600; cursor: pointer;
    display: flex; align-items: center; gap: 8px; transition: all 0.2s;
}
.add-btn:hover { background: var(--primary-dark); transform: translateY(-1px); }

/* --- Content & Empty State --- */
.content { max-width: 650px; margin: 40px auto; padding: 0 20px; min-height: 500px; }
.hidden { display: none !important; }

.empty-container {
    text-align: center; padding: 80px 20px;
    background: transparent; border: none;
    display: flex; flex-direction: column; align-items: center;
    margin-top: 20px;
}
.logo-box.big-logo { width: 70px; height: 70px; font-size: 2rem; margin-bottom: 20px; border-radius: 16px;}
.empty-container h2 { margin: 0 0 10px 0; color: var(--text-main); }
.empty-container p { color: var(--text-sub); margin: 0 0 25px 0; }
.big-btn { padding: 14px 30px; font-size: 1.05rem; }

/* --- Progress & Tools --- */
.progress-header { display: flex; justify-content: space-between; align-items: center; margin-bottom: 12px; color: var(--text-sub); font-size: 0.9rem; }

/* Tool Buttons (Reset, Edit, Delete) */
.tool-icon, #reset-deck {
    background: var(--card-bg);
    border: 1px solid var(--border);
    color: var(--text-sub);
    border-radius: 10px;
    padding: 8px 12px;
    transition: all 0.2s ease;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 600;
    gap: 8px;
}

#reset-deck { font-size: 0.9rem; }

/* Edit & Reset Hover (Light Blue) */
.blue-tool:hover, #reset-deck:hover {
    border-color: var(--primary); color: var(--primary);
    background: rgba(52, 152, 219, 0.05); transform: translateY(-2px);
}

/* Delete Hover (Light Red) */
.red-tool:hover {
    border-color: var(--danger); color: var(--danger);
    background: rgba(231, 76, 60, 0.05); transform: translateY(-2px);
}

.progress-bar-bg { height: 8px; background: var(--border); border-radius: 10px; overflow: hidden; margin-bottom: 35px; }
.progress-bar-fill { height: 100%; background: var(--primary); width: 0%; transition: width 0.4s ease; }

/* --- Flashcard --- */
.flashcard-wrapper { perspective: 1000px; }
.card { width: 100%; height: 380px; position: relative; transform-style: preserve-3d; transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1); }
.card.is-flipped { transform: rotateY(180deg); }
.card-face {
    position: absolute; width: 100%; height: 100%; backface-visibility: hidden;
    background: var(--card-bg); border-radius: 20px; box-shadow: var(--shadow-md);
    display: flex; flex-direction: column; padding: 35px; box-sizing: border-box; border: 1px solid var(--border);
}
.card-back { transform: rotateY(180deg); }
.card-header { display: flex; justify-content: space-between; width: 100%; margin-bottom: 20px; align-items: center;}

.card-tag {
    background: rgba(52, 152, 219, 0.1); color: var(--primary);
    padding: 6px 12px; border-radius: 6px;
    font-size: 0.75rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.5px;
}
.answer-tag { background: rgba(46, 204, 113, 0.1); color: var(--success); }

/* Tool Gap & Icon Size */
.card-tools { display: flex; gap: 12px; }
.tool-icon { width: 38px; height: 38px; font-size: 1rem; }

.card-body { flex-grow: 1; display: flex; align-items: center; justify-content: center; text-align: center; }
.card-body h2 { font-size: 1.6rem; line-height: 1.4; margin: 0; }

.reveal-btn {
    width: auto; margin: 0 auto; padding: 12px 25px; min-width: 180px;
    border: 2px solid var(--border); background: transparent; color: var(--text-main);
    border-radius: 50px; font-weight: 600; cursor: pointer; transition: 0.2s;
    display: flex; align-items: center; justify-content: center; gap: 8px;
}
.reveal-btn:hover { border-color: var(--success); color: var(--success); background: rgba(46, 204, 113, 0.05); }
.reveal-btn.back-btn:hover { border-color: var(--text-sub); color: var(--text-main); background: var(--border); }

/* --- Navigation --- */
.navigation-panel { display: flex; justify-content: center; gap: 15px; margin-top: 35px; }
.nav-btn {
    background: var(--card-bg); border: 1px solid var(--border); padding: 12px 25px;
    border-radius: 50px; font-weight: 600; color: var(--text-main); cursor: pointer;
    transition: all 0.2s; box-shadow: var(--shadow-sm); display: flex; align-items: center; gap: 8px;
}
.nav-btn:hover:not(:disabled) { border-color: var(--primary); color: var(--primary); transform: translateY(-2px); }
.nav-btn:disabled { opacity: 0.5; cursor: not-allowed; transform: none; box-shadow: none; }

/* --- Modals --- */
.modal {
    display: none; position: fixed; z-index: 200; top: 0; left: 0; width: 100%; height: 100%;
    background: rgba(0,0,0,0.5); backdrop-filter: blur(3px); justify-content: center; align-items: center; opacity: 0; transition: opacity 0.3s;
}
.modal.show { display: flex; opacity: 1; }
.modal-content {
    background: var(--card-bg); width: 90%; max-width: 500px; border-radius: 20px; padding: 30px;
    box-shadow: var(--shadow-md); transform: translateY(20px); transition: transform 0.3s;
}
.modal.show .modal-content { transform: translateY(0); }
.modal-header-styled { display: flex; justify-content: space-between; align-items: flex-start; margin-bottom: 25px; }
.modal-title-box { display: flex; gap: 15px; }
#modal-icon { font-size: 1.4rem; color: var(--primary); margin-top: 5px; }
.modal-title-box h3 { margin: 0 0 5px 0; font-size: 1.3rem; }
#modal-subtitle { margin: 0; color: var(--text-sub); font-size: 0.9rem; }
.close-x { background: none; border: none; font-size: 1.2rem; cursor: pointer; color: var(--text-sub); transition: 0.2s; }
.close-x:hover { color: var(--danger); }

.input-group { margin-bottom: 20px; }
.input-group label { display: block; font-size: 0.9rem; font-weight: 600; margin-bottom: 8px; color: var(--text-sub); }
input, textarea {
    width: 100%; padding: 14px 16px; border: 2px solid var(--border); border-radius: 12px;
    background: var(--bg-body); color: var(--text-main); font-family: inherit; font-size: 1rem;
    box-sizing: border-box; transition: 0.2s;
}
textarea { resize: vertical; min-height: 120px; }
input:focus, textarea:focus { border-color: var(--primary); outline: none; }

.modal-buttons { display: flex; justify-content: flex-end; gap: 12px; margin-top: 25px; }
.cancel-btn { background: transparent; border: none; color: var(--text-sub); font-weight: 600; cursor: pointer; padding: 12px 20px; border-radius: 8px; transition: 0.2s;}
.cancel-btn:hover { background: var(--border); color: var(--text-main); }
.save-btn { background: var(--primary); color: white; border: none; padding: 12px 24px; border-radius: 8px; font-weight: 600; cursor: pointer; transition: 0.2s; display: flex; align-items: center; gap: 8px;}
.save-btn:hover:not(:disabled) { background: var(--primary-dark); }
.save-btn:disabled { background: var(--border); color: var(--text-sub); cursor: not-allowed; opacity: 0.7;}

.delete-content { text-align: center; max-width: 380px; }
.delete-icon-area { 
    width: 70px; height: 70px; background: #fee2e2; color: var(--danger);
    border-radius: 50%; display: flex; align-items: center; justify-content: center;
    font-size: 1.8rem; margin: 0 auto 20px auto;
}
.delete-confirm-btn { background: var(--danger); color: white; border: none; padding: 12px 24px; border-radius: 8px; font-weight: 600; cursor: pointer; transition: 0.2s; }
.delete-confirm-btn:hover { background: #c0392b; }

#toast-container { position: fixed; top: 90px; right: 20px; z-index: 1000; display: flex; flex-direction: column; gap: 10px; }
.toast {
    min-width: 260px; padding: 16px 20px; border-radius: 10px; color: white; font-weight: 500;
    display: flex; align-items: center; gap: 12px; box-shadow: var(--shadow-md); animation: slideIn 0.3s ease-out forwards;
}
.toast.success { background: var(--success); }
.toast.error { background: var(--danger); }
@keyframes slideIn { from { transform: translateX(100%); opacity: 0; } to { transform: translateX(0); opacity: 1; } }