/* Modern CSS with latest features */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    /* CSS Custom Properties for consistent theming */
    --primary-bg: oklch(0.7 0.15 250);
    --secondary-bg: oklch(0.6 0.12 280);
    --text-primary: oklch(0.2 0.02 270);
    --text-light: oklch(0.95 0.02 270);
    --correct-bg: oklch(0.8 0.1 140);
    --incorrect-bg: oklch(0.7 0.15 20);
    --cursor-bg: oklch(0.7 0.12 220);
    --surface: oklch(0.98 0.01 270);
    --border: oklch(0.9 0.02 270);
    --focus-ring: oklch(0.7 0.12 220 / 0.2);
    
    /* Modern font stack with system fonts */
    --font-mono: ui-monospace, 'Cascadia Code', 'SF Mono', Monaco, 'Roboto Mono', monospace;
    --font-system: system-ui, -apple-system, sans-serif;
    
    /* Smooth animations */
    --transition-fast: 0.15s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-normal: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    --shadow-subtle: 0 1px 3px oklch(0 0 0 / 0.1), 0 1px 2px oklch(0 0 0 / 0.06);
    --shadow-moderate: 0 4px 6px oklch(0 0 0 / 0.07), 0 2px 4px oklch(0 0 0 / 0.06);
    --shadow-strong: 0 20px 25px oklch(0 0 0 / 0.1), 0 10px 10px oklch(0 0 0 / 0.04);
}

body {
    font-family: var(--font-system);
    background: linear-gradient(135deg, var(--primary-bg), var(--secondary-bg));
    min-height: 100vh;
    min-height: 100svh; /* Modern viewport units */
    color: var(--text-primary);
    /* Modern scrollbar styling */
    scrollbar-width: thin;
    scrollbar-color: var(--border) transparent;
}

/* Webkit scrollbar styling */
::-webkit-scrollbar {
    width: 8px;
}

::-webkit-scrollbar-track {
    background: transparent;
}

::-webkit-scrollbar-thumb {
    background: var(--border);
    border-radius: 4px;
}

.container {
    max-width: 900px;
    margin: 0 auto;
    padding: 20px;
    container-type: inline-size; /* Container queries support */
}

header {
    text-align: center;
    margin-bottom: 30px;
    color: var(--text-light);
}

header h1 {
    font-size: clamp(2rem, 5vw, 2.5rem); /* Responsive typography */
    margin-bottom: 10px;
    text-shadow: 0 2px 4px oklch(0 0 0 / 0.3);
    font-weight: 700;
}

header p {
    font-size: clamp(1rem, 3vw, 1.1rem);
    opacity: 0.9;
}

.stats {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: 1rem;
    background: var(--surface);
    border-radius: 16px;
    padding: 24px;
    margin-bottom: 30px;
    box-shadow: var(--shadow-moderate);
    backdrop-filter: blur(10px);
}

.stat {
    text-align: center;
    padding: 8px;
}

.stat-label {
    display: block;
    font-size: 0.875rem;
    color: oklch(0.5 0.02 270);
    margin-bottom: 8px;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    font-weight: 500;
}

.stat-value {
    display: block;
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-primary);
    font-variant-numeric: tabular-nums; /* Better number alignment */
}

.exercise-container {
    background: var(--surface);
    border-radius: 16px;
    padding: 32px;
    margin-bottom: 30px;
    box-shadow: var(--shadow-moderate);
    backdrop-filter: blur(10px);
    border: 1px solid oklch(0 0 0 / 0.05);
}

.exercise-info h2 {
    color: var(--text-primary);
    margin-bottom: 20px;
    font-size: 1.25rem;
    font-weight: 600;
}

.code-display {
    background: oklch(0.15 0.02 270);
    border-radius: 12px;
    padding: 24px;
    margin-bottom: 20px;
    overflow-x: auto;
    border: 1px solid oklch(0.2 0.02 270);
    position: relative;
}

.code-to-type {
    font-family: var(--font-mono);
    font-size: 1.125rem;
    line-height: 1.6;
    color: oklch(0.85 0.02 270);
    white-space: pre;
    font-variant-ligatures: common-ligatures; /* Enable font ligatures */
}

/* UPDATED: Light green background for correct characters */
.code-to-type .correct {
    background-color: var(--correct-bg);
    color: oklch(0.15 0.02 270);
    border-radius: 3px;
    padding: 1px 2px;
    box-shadow: inset 0 1px 2px oklch(0 0 0 / 0.1);
}

.code-to-type .incorrect {
    background-color: var(--incorrect-bg);
    color: var(--text-light);
    border-radius: 3px;
    padding: 1px 2px;
    box-shadow: inset 0 1px 2px oklch(0 0 0 / 0.2);
    animation: shake 0.3s ease-in-out;
}

.code-to-type .cursor-char {
    background-color: var(--cursor-bg);
    color: var(--text-light);
    border-radius: 3px;
    padding: 1px 2px;
    animation: pulse 1.5s ease-in-out infinite;
}

/* Modern animations using @property for smooth transitions */
@keyframes pulse {
    0%, 100% { 
        opacity: 1; 
        transform: scale(1);
    }
    50% { 
        opacity: 0.7; 
        transform: scale(1.02);
    }
}

@keyframes shake {
    0%, 100% { transform: translateX(0); }
    25% { transform: translateX(-2px); }
    75% { transform: translateX(2px); }
}

.input-container {
    margin-bottom: 20px;
    position: relative;
}

#user-input {
    width: 100%;
    padding: 16px;
    font-family: var(--font-mono);
    font-size: 1.125rem;
    border: 2px solid var(--border);
    border-radius: 12px;
    outline: none;
    transition: all var(--transition-normal);
    background: var(--surface);
    color: var(--text-primary);
    resize: none; /* For textarea if upgraded */
}

#user-input:focus {
    border-color: var(--cursor-bg);
    box-shadow: 0 0 0 4px var(--focus-ring);
    transform: translateY(-1px);
}

/* Modern focus-visible for better accessibility */
#user-input:focus-visible {
    outline: 2px solid var(--cursor-bg);
    outline-offset: 2px;
}

.feedback {
    min-height: 40px;
    font-size: 1rem;
    font-weight: 500;
    text-align: center;
    padding: 12px 16px;
    border-radius: 8px;
    margin-bottom: 12px;
    border: 1px solid transparent;
    transition: all var(--transition-normal);
    font-family: var(--font-system);
}

.feedback.success {
    background: oklch(0.9 0.05 140);
    color: oklch(0.25 0.08 140);
    border-color: oklch(0.8 0.08 140);
}

.feedback.error {
    background: oklch(0.9 0.05 20);
    color: oklch(0.3 0.08 20);
    border-color: oklch(0.8 0.08 20);
}

.feedback.info {
    background: oklch(0.9 0.05 220);
    color: oklch(0.3 0.08 220);
    border-color: oklch(0.8 0.08 220);
}

/* NEW: Navigation hint styling */
.feedback.navigation-hint {
    background: oklch(0.95 0.03 280);
    color: oklch(0.25 0.05 280);
    border-color: oklch(0.8 0.05 280);
    border-left: 4px solid oklch(0.6 0.08 280);
    text-align: left;
    font-family: var(--font-mono);
    font-size: 0.9rem;
    animation: slideIn 0.3s ease-out;
}

.feedback.navigation-hint .shortcut-key {
    background: oklch(0.2 0.02 280);
    color: var(--text-light);
    padding: 2px 6px;
    border-radius: 4px;
    font-weight: 600;
    margin: 0 2px;
    font-size: 0.85rem;
}

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

.controls {
    display: flex;
    gap: 16px;
    justify-content: center;
    margin-bottom: 30px;
    flex-wrap: wrap;
}

.btn {
    padding: 12px 24px;
    border: none;
    border-radius: 8px;
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-normal);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    font-family: var(--font-system);
    position: relative;
    overflow: hidden;
}

.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none !important;
}

.btn-primary {
    background: linear-gradient(135deg, var(--cursor-bg), oklch(0.6 0.12 240));
    color: var(--text-light);
    box-shadow: var(--shadow-subtle);
}

.btn-primary:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: var(--shadow-strong);
    filter: brightness(1.1);
}

.btn-primary:active:not(:disabled) {
    transform: translateY(0);
    transition-duration: 0.1s;
}

.btn-secondary {
    background: var(--surface);
    color: var(--text-primary);
    border: 1px solid var(--border);
    box-shadow: var(--shadow-subtle);
}
}

.btn-secondary:hover {
    background: #cbd5e0;
    transform: translateY(-2px);
}

.btn-secondary:hover:not(:disabled) {
    transform: translateY(-1px);
    box-shadow: var(--shadow-moderate);
    border-color: oklch(0.7 0.05 270);
}

.progress-container {
    background: var(--surface);
    border-radius: 16px;
    padding: 24px;
    box-shadow: var(--shadow-moderate);
    backdrop-filter: blur(10px);
}

.progress-bar {
    background: var(--border);
    border-radius: 12px;
    height: 12px;
    overflow: hidden;
    position: relative;
}

.progress-fill {
    background: linear-gradient(135deg, var(--correct-bg), oklch(0.7 0.12 140));
    height: 100%;
    border-radius: 12px;
    transition: width var(--transition-normal);
    width: 0%;
    position: relative;
}

.progress-fill::after {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: linear-gradient(90deg, transparent, oklch(1 0 0 / 0.3), transparent);
    animation: shimmer 2s infinite;
}

@keyframes shimmer {
    0% { transform: translateX(-100%); }
    100% { transform: translateX(100%); }
}

/* Modern responsive design with container queries */
@container (max-width: 768px) {
    .stats {
        grid-template-columns: repeat(2, 1fr);
        gap: 0.75rem;
        padding: 20px;
    }
    
    .controls {
        flex-direction: column;
        align-items: center;
        gap: 12px;
    }
    
    .btn {
        width: min(200px, 100%);
    }
}

/* Reduced motion support */
@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}

/* Dark mode support */
@media (prefers-color-scheme: dark) {
    :root {
        --surface: oklch(0.15 0.02 270);
        --text-primary: oklch(0.85 0.02 270);
        --text-light: oklch(0.95 0.02 270);
        --border: oklch(0.25 0.02 270);
    }
}