* { box-sizing: border-box; }

.problem-card {
    background: white;
    border-radius: 20px;
    box-shadow: 0 8px 32px rgba(0,0,0,0.06);
    overflow: hidden;
    margin-bottom: 28px;
    border: 1px solid rgba(0,0,0,0.04);
}
.problem-card .problem-header {
    color: white;
    padding: 22px 28px;
    position: relative;
    overflow: hidden;
}
.problem-card .problem-header::after {
    content: '';
    position: absolute;
    top: -50%;
    right: -20%;
    width: 200px;
    height: 200px;
    background: rgba(255,255,255,0.06);
    border-radius: 50%;
}
.problem-card .problem-header h1 {
    font-size: 1.25em;
    font-weight: 700;
    margin: 0;
    position: relative;
    z-index: 1;
    letter-spacing: -0.01em;
}
.problem-card .problem-content { padding: 28px; }
#problem-content {
    font-size: 1.08em;
    line-height: 1.75;
    color: #1e293b;
}
#problem-content strong {
    color: #0f172a;
    font-weight: 700;
}

.audio-play-btn {
    display: inline-flex;
    align-items: center;
    gap: 10px;
    padding: 12px 24px;
    color: white;
    border: none;
    border-radius: 50px;
    cursor: pointer;
    font-size: 0.95em;
    font-weight: 600;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    margin: 12px 0;
    box-shadow: 0 4px 14px rgba(0,0,0,0.15);
    letter-spacing: 0.02em;
}
.audio-play-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(0,0,0,0.2);
}
.audio-play-btn:active { transform: translateY(0); }
.audio-play-btn i { font-size: 1.15em; }

.answer-section {
    background: white;
    border-radius: 20px;
    box-shadow: 0 8px 32px rgba(0,0,0,0.06);
    padding: 28px;
    margin-bottom: 28px;
    border: 1px solid rgba(0,0,0,0.04);
}
.answer-section h2 {
    font-size: 1.05em;
    font-weight: 700;
    margin-bottom: 18px;
    letter-spacing: -0.01em;
}

.mcq-container { display: flex; flex-direction: column; gap: 10px; }
.mcq-option {
    display: flex;
    align-items: center;
    gap: 14px;
    padding: 16px 20px;
    border: 2px solid #e2e8f0;
    border-radius: 14px;
    cursor: pointer;
    transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
    background: #fafbfc;
    font-size: 1.05em;
    position: relative;
}
.mcq-option::before {
    content: '';
    width: 22px;
    height: 22px;
    border-radius: 50%;
    border: 2px solid #cbd5e1;
    flex-shrink: 0;
    transition: all 0.2s;
    background: white;
}
.mcq-option:hover {
    border-color: #94a3b8;
    background: #f8fafc;
    transform: translateX(4px);
}
.mcq-option.selected::before {
    border-width: 6px;
}
.mcq-option.correct {
    border-color: #22c55e;
    background: linear-gradient(135deg, #f0fdf4, #dcfce7);
}
.mcq-option.correct::before {
    border-color: #22c55e;
    background: #22c55e;
    box-shadow: inset 0 0 0 3px white;
}
.mcq-option.incorrect {
    border-color: #ef4444;
    background: linear-gradient(135deg, #fef2f2, #fee2e2);
}
.mcq-option.incorrect::before {
    border-color: #ef4444;
    background: #ef4444;
    box-shadow: inset 0 0 0 3px white;
}
.mcq-option input[type="radio"] { display: none; }
.mcq-option label {
    cursor: pointer;
    margin: 0;
    flex: 1;
    line-height: 1.5;
    font-weight: 450;
    color: #334155;
}

.sorting-list { list-style: none; padding: 0; margin: 0; }
.sorting-item {
    display: flex;
    align-items: center;
    gap: 14px;
    padding: 16px 20px;
    border: 2px solid #e2e8f0;
    border-radius: 14px;
    margin-bottom: 8px;
    background: #fafbfc;
    cursor: grab;
    transition: all 0.2s;
    user-select: none;
    font-size: 1.05em;
}
.sorting-item:active { cursor: grabbing; box-shadow: 0 8px 25px rgba(0,0,0,0.12); }
.sorting-item .drag-handle { color: #94a3b8; font-size: 1.1em; }
.sorting-item .step-number {
    color: white;
    width: 30px;
    height: 30px;
    border-radius: 10px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
    font-size: 0.85em;
    flex-shrink: 0;
}
.sorting-item.correct { border-color: #22c55e; background: linear-gradient(135deg, #f0fdf4, #dcfce7); }
.sorting-item.incorrect { border-color: #ef4444; background: linear-gradient(135deg, #fef2f2, #fee2e2); }
.sorting-item.dragging { opacity: 0.4; transform: scale(0.98); }

.classification-zone {
    border: 2px dashed #cbd5e1;
    border-radius: 16px;
    padding: 18px;
    min-height: 80px;
    margin-bottom: 15px;
    transition: all 0.25s;
    background: #fafbfc;
}
.classification-zone.drag-over {
    background: #f0fdf4;
    border-color: #86efac;
    box-shadow: 0 0 0 4px rgba(34,197,94,0.1);
}
.classification-zone h4 { font-size: 0.95em; font-weight: 700; margin-bottom: 10px; }
.classification-item {
    display: inline-block;
    padding: 10px 18px;
    border: 2px solid #e2e8f0;
    border-radius: 10px;
    margin: 4px;
    background: white;
    cursor: grab;
    transition: all 0.2s;
    font-size: 1.05em;
    font-weight: 500;
    box-shadow: 0 2px 4px rgba(0,0,0,0.04);
}
.classification-item:active { cursor: grabbing; }
.classification-item.correct { border-color: #22c55e; background: #f0fdf4; }
.classification-item.incorrect { border-color: #ef4444; background: #fef2f2; }
.classification-item.dragging { opacity: 0.4; }

.dd-source-zone,
.dd-drop-zone {
    border: 2px dashed #cbd5e1;
    border-radius: 16px;
    padding: 18px;
    min-height: 80px;
    margin-bottom: 15px;
    transition: all 0.25s;
    background: #fafbfc;
}
.dd-source-zone.drag-over,
.dd-drop-zone.drag-over {
    background: #f0fdf4;
    border-color: #86efac;
}
.dd-source-zone h4,
.dd-drop-zone h4 { font-size: 0.95em; font-weight: 700; margin-bottom: 10px; }
.dd-item {
    display: inline-block;
    padding: 10px 18px;
    border: 2px solid #e2e8f0;
    border-radius: 10px;
    margin: 4px;
    background: white;
    cursor: grab;
    transition: all 0.2s;
    font-size: 1.05em;
    font-weight: 500;
    box-shadow: 0 2px 4px rgba(0,0,0,0.04);
}
.dd-item:active { cursor: grabbing; }
.dd-item.correct { border-color: #22c55e; background: #f0fdf4; }
.dd-item.incorrect { border-color: #ef4444; background: #fef2f2; }
.dd-item.dragging { opacity: 0.4; }

.sb-target-zone {
    border: 2px dashed #86efac;
    border-radius: 16px;
    padding: 18px;
    min-height: 60px;
    margin-bottom: 15px;
    background: linear-gradient(135deg, #f0fdf4, #ecfdf5);
    transition: all 0.25s;
}
.sb-placeholder { color: #94a3b8; font-style: italic; text-align: center; padding: 10px; }
.sb-word-bank {
    border: 2px solid #e2e8f0;
    border-radius: 16px;
    padding: 18px;
    min-height: 50px;
    background: #fafbfc;
}
.sb-word {
    display: inline-block;
    padding: 10px 18px;
    border: 2px solid #3b82f6;
    border-radius: 10px;
    margin: 4px;
    background: linear-gradient(135deg, #eff6ff, #dbeafe);
    cursor: grab;
    transition: all 0.2s;
    font-size: 1.05em;
    font-weight: 600;
    color: #1e40af;
    box-shadow: 0 2px 8px rgba(59,130,246,0.12);
}
.sb-word:hover {
    background: linear-gradient(135deg, #dbeafe, #bfdbfe);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(59,130,246,0.2);
}
.sb-word:active { cursor: grabbing; transform: translateY(0); }

.action-buttons {
    display: flex;
    gap: 12px;
    margin-top: 24px;
    flex-wrap: wrap;
}
.btn-lang {
    padding: 13px 28px;
    border-radius: 12px;
    font-weight: 650;
    border: none;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    font-size: 0.92em;
    letter-spacing: 0.02em;
    display: inline-flex;
    align-items: center;
    gap: 8px;
}
.btn-check-ans {
    color: white;
    box-shadow: 0 4px 14px rgba(0,0,0,0.15);
}
.btn-check-ans:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(0,0,0,0.2);
    color: white;
}
.btn-check-ans:active { transform: translateY(0); }
.btn-tip { border: 2px solid; }
.btn-next { border: 2px solid; }

#feedback-area {
    margin-top: 18px;
    padding: 16px 22px;
    border-radius: 14px;
    display: none;
    font-weight: 650;
    font-size: 0.95em;
    letter-spacing: 0.01em;
}
#feedback-area.correct {
    display: block;
    background: linear-gradient(135deg, #f0fdf4, #dcfce7);
    color: #15803d;
    border: 2px solid #86efac;
}
#feedback-area.incorrect {
    display: block;
    background: linear-gradient(135deg, #fef2f2, #fee2e2);
    color: #b91c1c;
    border: 2px solid #fca5a5;
}

.sidebar-card {
    background: white;
    border-radius: 20px;
    box-shadow: 0 8px 32px rgba(0,0,0,0.06);
    overflow: hidden;
    margin-bottom: 22px;
    border: 1px solid rgba(0,0,0,0.04);
}
.sidebar-card .card-head {
    padding: 16px 22px;
    font-weight: 700;
    font-size: 0.92em;
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
    color: white;
    letter-spacing: 0.03em;
    text-transform: uppercase;
}
.sidebar-card .card-body-inner { padding: 0 22px 22px; }

.score-display { text-align: center; padding: 24px 20px; }
.score-number {
    font-size: 3.5em;
    font-weight: 800;
    line-height: 1;
    letter-spacing: -0.02em;
}
.score-label {
    color: #94a3b8;
    font-size: 0.82em;
    margin-top: 6px;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    font-weight: 600;
}
.score-bar {
    height: 6px;
    background: #e2e8f0;
    border-radius: 3px;
    margin-top: 18px;
    overflow: hidden;
}
.score-fill {
    height: 100%;
    border-radius: 3px;
    transition: width 0.6s cubic-bezier(0.4, 0, 0.2, 1);
}

#remember-content {
    font-size: 1.4em;
    line-height: 1.75;
    color: #334155;
}
#remember-content h4 {
    font-weight: 700;
    margin-bottom: 12px;
    font-size: 0.85em;
}
#remember-content li { margin-bottom: 6px; }
#remember-content table {
    width: 100%;
    border-collapse: separate;
    border-spacing: 0;
    font-size: 0.85em;
}
#remember-content table th {
    padding: 10px 14px;
    font-weight: 700;
    text-align: left;
    border-bottom: 2px solid #e2e8f0;
}
#remember-content table td {
    padding: 8px 14px;
    border-bottom: 1px solid #f1f5f9;
}
#remember-content table tr:last-child td { border-bottom: none; }

#solution-panel {
    display: none;
    padding: 28px;
    margin: 0 0 28px;
    border-radius: 16px;
    position: relative;
    overflow: hidden;
}
#solution-panel::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    width: 5px;
    border-radius: 5px 0 0 5px;
}
#solution-panel h4 {
    font-weight: 700;
    margin-bottom: 15px;
    font-size: 1.05em;
}
#solution-panel p, #solution-panel div { font-size: 1.02em; line-height: 1.7; }

.loading-spinner { text-align: center; padding: 48px; color: #94a3b8; }
.loading-spinner i { font-size: 2em; margin-bottom: 12px; }

.skill-practice-lang { padding: 28px 0; }

.lang-breadcrumbs {
    padding: 0;
    border-bottom: 1px solid rgba(0,0,0,0.06);
}
.lang-breadcrumbs .container-fluid {
    padding-top: 14px;
    padding-bottom: 14px;
}
.lang-breadcrumbs .breadcrumb {
    background: none;
    margin: 0;
    padding: 0;
    font-size: 0.88em;
    font-weight: 500;
}
.lang-breadcrumbs .breadcrumb a { text-decoration: none; }

@keyframes svgPulse {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.1); }
}
@keyframes svgBounce {
    0%, 100% { transform: translateY(0); }
    50% { transform: translateY(-10px); }
}
@keyframes fadeInUp {
    from { opacity: 0; transform: translateY(12px); }
    to { opacity: 1; transform: translateY(0); }
}

@media (max-width: 991px) {
    .skill-practice-lang { padding: 16px 0; }
    .problem-card .problem-content { padding: 20px; }
    .answer-section { padding: 20px; }
    .action-buttons { flex-direction: column; }
    .btn-lang { width: 100%; justify-content: center; }
}