:root {
    --primary: #4A6FFF;
    --primary-hover: #3A5BDE;
    --success: #00C48C;
    --danger: #FF647C;
    --background: #F4F7FE;
    --card-bg: #FFFFFF;
    --text-main: #2B3674;
    --text-muted: #A3AED0;
    --border: #E2E8F0;
    --shadow: 0 4px 20px rgba(0, 0, 0, 0.05);
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    -webkit-tap-highlight-color: transparent;
}

body {
    background-color: var(--background);
    color: var(--text-main);
    display: flex;
    justify-content: center;
    min-height: 100vh;
}

#app {
    width: 100%;
    max-width: 480px; /* Mobile constraint */
    background: var(--background);
    position: relative;
    min-height: 100vh;
    box-shadow: 0 0 40px rgba(0,0,0,0.05);
}

/* Screens */
.screen {
    display: none;
    flex-direction: column;
    min-height: 100vh;
    width: 100%;
    background: var(--background);
    animation: fadeIn 0.3s ease;
}

.screen.active {
    display: flex;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

@keyframes slideIn {
    from { transform: translateX(100%); }
    to { transform: translateX(0); }
}

/* Home Screen */
#home-screen header {
    padding: 40px 20px;
    text-align: center;
}

#home-screen h1 {
    font-size: 28px;
    font-weight: 700;
    color: var(--primary);
    margin-bottom: 8px;
}

#home-screen p {
    color: var(--text-muted);
    font-size: 14px;
}

#home-screen main {
    padding: 0 20px;
    flex-grow: 1;
}

.stats-card {
    background: var(--card-bg);
    border-radius: 20px;
    padding: 24px;
    box-shadow: var(--shadow);
    margin-bottom: 24px;
}

.stats-card h2 {
    font-size: 16px;
    margin-bottom: 16px;
    color: var(--text-main);
}

.stats-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
}

.stat-box {
    background: var(--background);
    padding: 16px;
    border-radius: 12px;
    text-align: center;
}

.stat-label {
    display: block;
    font-size: 12px;
    color: var(--text-muted);
    margin-bottom: 4px;
}

.stat-value {
    display: block;
    font-size: 20px;
    font-weight: 700;
    color: var(--primary);
}

.weakness-alert {
    background: rgba(255, 100, 124, 0.1);
    color: var(--danger);
    padding: 16px;
    border-radius: 12px;
    margin-bottom: 24px;
    border: 1px solid rgba(255, 100, 124, 0.2);
}

.weakness-alert strong {
    display: block;
    margin-bottom: 4px;
}

/* Settings Form */
.settings-card {
    background: var(--card-bg);
    border-radius: 20px;
    padding: 24px;
    box-shadow: var(--shadow);
    margin-bottom: 24px;
}

.settings-card h2 {
    font-size: 16px;
    margin-bottom: 16px;
    color: var(--text-main);
}

.setting-group {
    margin-bottom: 16px;
}

.setting-group label {
    display: block;
    font-size: 13px;
    color: var(--text-muted);
    margin-bottom: 8px;
    font-weight: 500;
}

.setting-group select {
    width: 100%;
    padding: 12px 16px;
    border: 2px solid var(--border);
    border-radius: 12px;
    font-size: 15px;
    color: var(--text-main);
    background-color: var(--background);
    outline: none;
    appearance: none;
    cursor: pointer;
}

.setting-group select:focus {
    border-color: var(--primary);
}

/* Buttons */
.primary-btn {
    width: 100%;
    background: var(--primary);
    color: white;
    border: none;
    padding: 16px;
    font-size: 16px;
    font-weight: 600;
    border-radius: 16px;
    cursor: pointer;
    transition: transform 0.1s, background 0.2s;
    box-shadow: 0 4px 15px rgba(74, 111, 255, 0.3);
}

.primary-btn:active {
    transform: scale(0.98);
    background: var(--primary-hover);
}

.secondary-btn {
    width: 100%;
    background: transparent;
    color: var(--text-muted);
    border: none;
    padding: 16px;
    font-size: 16px;
    font-weight: 500;
    margin-top: 8px;
    cursor: pointer;
}

/* Quiz Screen */
.quiz-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 20px;
    background: var(--card-bg);
    box-shadow: 0 2px 10px rgba(0,0,0,0.02);
}

.category-badge {
    background: rgba(74, 111, 255, 0.1);
    color: var(--primary);
    padding: 6px 12px;
    border-radius: 20px;
    font-size: 12px;
    font-weight: 600;
}

.timer-container {
    display: flex;
    align-items: center;
    gap: 12px;
}

.timer {
    font-variant-numeric: tabular-nums;
    font-size: 18px;
    font-weight: 700;
    color: var(--text-main);
}

.icon-btn {
    background: rgba(0, 0, 0, 0.05);
    border: none;
    border-radius: 50%;
    width: 36px;
    height: 36px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    font-size: 16px;
    transition: background 0.2s;
}

.icon-btn:hover {
    background: rgba(0, 0, 0, 0.1);
}

.quiz-main {
    padding: 24px 20px;
    display: flex;
    flex-direction: column;
    flex-grow: 1;
}

.question-container {
    background: var(--card-bg);
    padding: 24px;
    border-radius: 20px;
    box-shadow: var(--shadow);
    margin-bottom: 24px;
    font-size: 16px;
    line-height: 1.6;
    color: var(--text-main);
}

.options-container {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.option-btn {
    background: var(--card-bg);
    border: 2px solid var(--border);
    padding: 16px 20px;
    border-radius: 16px;
    font-size: 15px;
    font-weight: 500;
    text-align: left;
    color: var(--text-main);
    cursor: pointer;
    transition: all 0.2s;
    position: relative;
    overflow: hidden;
}

.option-btn:hover {
    border-color: var(--primary);
    background: rgba(74, 111, 255, 0.02);
}

.option-btn:active {
    transform: scale(0.98);
}

.option-btn.correct {
    border-color: var(--success);
    color: var(--success);
    background: rgba(0, 196, 140, 0.05);
}

.option-btn.incorrect {
    border-color: var(--danger);
    color: var(--danger);
    background: rgba(255, 100, 124, 0.05);
}

/* Result Screen */
.result-header {
    padding: 30px 20px;
    text-align: center;
    color: white;
}

.result-header.success {
    background: var(--success);
}

.result-header.error {
    background: var(--danger);
}

#result-title {
    font-size: 24px;
    font-weight: 700;
}

.result-main {
    padding: 24px 20px;
    flex-grow: 1;
    display: flex;
    flex-direction: column;
}

.explanation-card {
    background: var(--card-bg);
    border-radius: 20px;
    padding: 24px;
    box-shadow: var(--shadow);
    margin-bottom: auto;
}

.explanation-card h3 {
    font-size: 14px;
    color: var(--text-muted);
    margin-bottom: 12px;
    text-transform: uppercase;
    letter-spacing: 1px;
}

#explanation-text {
    font-size: 15px;
    line-height: 1.7;
    white-space: pre-wrap;
    color: var(--text-main);
}

.result-actions {
    margin-top: 30px;
    padding-bottom: 20px;
}

/* Summary Screen */
.summary-header {
    background: var(--primary);
    padding: 30px 20px;
    text-align: center;
    color: white;
}

.summary-score {
    font-size: 32px;
    font-weight: 700;
    margin-top: 8px;
}

.summary-main {
    padding: 24px 20px;
    flex-grow: 1;
}

.summary-item {
    background: var(--card-bg);
    border-radius: 16px;
    padding: 20px;
    margin-bottom: 16px;
    box-shadow: var(--shadow);
    border-left: 6px solid var(--border);
}

.summary-item.correct {
    border-left-color: var(--success);
}

.summary-item.incorrect {
    border-left-color: var(--danger);
}

.summary-item .meta {
    font-size: 12px;
    color: var(--text-muted);
    margin-bottom: 8px;
    display: flex;
    justify-content: space-between;
}

.summary-item .q-text {
    font-size: 14px;
    color: var(--text-main);
    margin-bottom: 12px;
    line-height: 1.5;
}

.summary-item .q-exp {
    font-size: 13px;
    color: var(--text-muted);
    background: var(--background);
    padding: 12px;
    border-radius: 8px;
    white-space: pre-wrap;
}

.mt-24 {
    margin-top: 24px;
}