/* CSS Custom Properties for Theme Colors */
:root {
    --primary-green: #00D4AA;
    --focus-blue: #4A90E2;
    --bg-gradient-start: #667eea;
    --bg-gradient-end: #764ba2;
    --bg-soft-white: #FAFAFA;
    --text-dark: #1a1a1a;
    --accent-orange: #FF6B35;
    --success-light-green: #00D4AA;
    --white: #FFFFFF;
    --light-gray: #F8F9FA;
    --medium-gray: #E9ECEF;
    --border-gray: #DEE2E6;
    --shadow-color: rgba(0, 0, 0, 0.08);
    --shadow-hover: rgba(0, 0, 0, 0.12);
    --glass-bg: rgba(255, 255, 255, 0.25);
    --glass-border: rgba(255, 255, 255, 0.18);
    --glass-shadow: 0 8px 32px 0 rgba(31, 38, 135, 0.37);

    /* Typography */
    --font-primary: 'Poppins', sans-serif;
    --font-secondary: 'Open Sans', sans-serif;

    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-xxl: 3rem;

    /* Border Radius */
    --radius-sm: 12px;
    --radius-md: 16px;
    --radius-lg: 20px;
    --radius-xl: 28px;
}

/* Dark Mode Variables */
[data-theme="dark"] {
    --primary-green: #00F5D4;
    --focus-blue: #74B9FF;
    --bg-gradient-start: #2D3436;
    --bg-gradient-end: #636E72;
    --bg-soft-white: #2D3436;
    --text-dark: #F8F9FA;
    --accent-orange: #FF7675;
    --success-light-green: #00F5D4;
    --white: #2D3436;
    --light-gray: #636E72;
    --medium-gray: #636E72;
    --border-gray: #636E72;
    --shadow-color: rgba(0, 0, 0, 0.3);
    --shadow-hover: rgba(0, 0, 0, 0.4);
    --glass-bg: rgba(45, 52, 54, 0.8);
    --glass-border: rgba(255, 255, 255, 0.1);
    --glass-shadow: 0 8px 32px 0 rgba(0, 0, 0, 0.5);
}

/* Reset and Base Styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: var(--font-secondary);
    background: linear-gradient(135deg, var(--bg-gradient-start) 0%, var(--bg-gradient-end) 100%);
    background-attachment: fixed;
    color: var(--text-dark);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    min-height: 100vh;
}

/* Container and Layout */
.container {
    max-width: 480px;
    margin: 0 auto;
    padding: var(--spacing-md);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* Header */
.header {
    margin-bottom: var(--spacing-xl);
    padding: var(--spacing-lg) 0;
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    max-width: 480px;
    margin: 0 auto;
}

.logo-section {
    text-align: center;
    flex: 1;
}

/* Theme Toggle */
.theme-toggle {
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border: 1px solid var(--glass-border);
    border-radius: 50%;
    width: 50px;
    height: 50px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: 0 4px 12px var(--shadow-color);
    position: relative;
    overflow: hidden;
}

.theme-toggle:hover {
    transform: scale(1.1);
    box-shadow: 0 6px 20px var(--shadow-hover);
}

.theme-toggle::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: linear-gradient(135deg, var(--primary-green), var(--focus-blue));
    opacity: 0;
    transition: opacity 0.3s ease;
}

.theme-toggle:hover::before {
    opacity: 0.1;
}

.theme-icon {
    font-size: 1.5rem;
    z-index: 1;
    transition: transform 0.3s ease;
}

.theme-toggle:hover .theme-icon {
    transform: rotate(15deg);
}

.logo {
    font-family: var(--font-primary);
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--primary-green);
    margin-bottom: var(--spacing-sm);
    text-shadow: 0 2px 4px var(--shadow-color);
}

.subtitle {
    font-size: 1rem;
    color: var(--text-dark);
    opacity: 0.8;
    font-weight: 400;
}

/* Main Content */
.main {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

/* Card Components */
.card {
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    box-shadow: var(--glass-shadow);
    border: 1px solid var(--glass-border);
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
}

.card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 2px;
    background: linear-gradient(90deg, var(--primary-green), var(--focus-blue), var(--accent-orange));
    opacity: 0;
    transition: opacity 0.3s ease;
}

.card:hover {
    box-shadow: 0 12px 40px rgba(0, 0, 0, 0.15);
    transform: translateY(-4px);
}

.card:hover::before {
    opacity: 1;
}

.card-header {
    text-align: center;
    margin-bottom: var(--spacing-lg);
}

.card-header h2 {
    font-family: var(--font-primary);
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--text-dark);
    margin-bottom: var(--spacing-sm);
}

.card-header p {
    font-size: 0.95rem;
    color: var(--text-dark);
    opacity: 0.7;
}

/* Interval Grid */
.interval-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-xl);
}

.interval-btn {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-lg);
    border: 2px solid var(--glass-border);
    background: var(--glass-bg);
    backdrop-filter: blur(5px);
    -webkit-backdrop-filter: blur(5px);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    font-family: var(--font-primary);
    min-height: 80px;
    position: relative;
    overflow: hidden;
    box-shadow: 0 2px 8px var(--shadow-color);
}

.interval-btn::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: linear-gradient(135deg, var(--primary-green), var(--focus-blue));
    opacity: 0;
    transition: opacity 0.3s ease;
    z-index: -1;
}

.interval-btn:hover {
    border-color: var(--primary-green);
    transform: translateY(-4px) scale(1.02);
    box-shadow: 0 8px 25px rgba(0, 212, 170, 0.3);
}

.interval-btn.selected {
    border-color: var(--primary-green);
    color: var(--white);
    transform: scale(1.05);
    box-shadow: 0 6px 20px rgba(0, 212, 170, 0.4);
}

.interval-btn.selected::before {
    opacity: 1;
}

.interval-btn.selected::after {
    content: '✓';
    position: absolute;
    top: var(--spacing-xs);
    right: var(--spacing-xs);
    font-size: 0.8rem;
    font-weight: bold;
    color: var(--white);
}

.interval-time {
    font-size: 1.5rem;
    font-weight: 700;
    line-height: 1;
}

.interval-unit {
    font-size: 0.85rem;
    font-weight: 500;
    opacity: 0.8;
    margin-top: var(--spacing-xs);
}

/* Control Buttons */
.control-buttons {
    display: flex;
    gap: var(--spacing-md);
    justify-content: center;
}

.btn {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-md) var(--spacing-lg);
    border: none;
    border-radius: var(--radius-md);
    font-family: var(--font-primary);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    min-width: 140px;
    min-height: 48px;
    position: relative;
    overflow: hidden;
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
}

.btn::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.2), transparent);
    transition: left 0.5s ease;
}

.btn:hover::before {
    left: 100%;
}

.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none;
    box-shadow: none;
}

.btn-primary {
    background: linear-gradient(135deg, var(--primary-green), #00b894);
    color: var(--white);
}

.btn-primary:hover:not(:disabled) {
    transform: translateY(-3px);
    box-shadow: 0 8px 25px rgba(0, 212, 170, 0.4);
}

.btn-secondary {
    background: linear-gradient(135deg, var(--accent-orange), #ff5722);
    color: var(--white);
}

.btn-secondary:hover:not(:disabled) {
    transform: translateY(-3px);
    box-shadow: 0 8px 25px rgba(255, 107, 53, 0.4);
}

.btn-icon {
    font-size: 1.1rem;
}

/* Status Card */
.status-info {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.status-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-sm) 0;
    border-bottom: 1px solid var(--medium-gray);
}

.status-item:last-child {
    border-bottom: none;
}

.status-label {
    font-weight: 600;
    color: var(--text-dark);
    opacity: 0.8;
}

.status-value {
    font-weight: 500;
    color: var(--focus-blue);
}

/* Gamification Section */
.gamification-section {
    margin-top: var(--spacing-lg);
    padding-top: var(--spacing-lg);
    border-top: 1px solid var(--glass-border);
}

.streak-display {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-lg);
    padding: var(--spacing-md);
    background: var(--glass-bg);
    backdrop-filter: blur(5px);
    -webkit-backdrop-filter: blur(5px);
    border-radius: var(--radius-md);
    border: 1px solid var(--glass-border);
}

.streak-icon {
    font-size: 2rem;
    animation: pulse 2s ease-in-out infinite;
}

.streak-info {
    display: flex;
    flex-direction: column;
}

.streak-label {
    font-size: 0.85rem;
    color: var(--text-dark);
    opacity: 0.7;
    font-weight: 500;
}

.streak-value {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--accent-orange);
}

.progress-section {
    background: var(--glass-bg);
    backdrop-filter: blur(5px);
    -webkit-backdrop-filter: blur(5px);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    border: 1px solid var(--glass-border);
}

.progress-label {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-sm);
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-dark);
}

.progress-bar {
    width: 100%;
    height: 8px;
    background: var(--medium-gray);
    border-radius: 4px;
    overflow: hidden;
    box-shadow: inset 0 1px 2px rgba(0, 0, 0, 0.1);
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--primary-green), var(--focus-blue));
    border-radius: 4px;
    transition: width 0.8s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
}

.progress-fill::after {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.3), transparent);
    animation: shimmer 2s ease-in-out infinite;
}

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

/* History Section */
.history-controls {
    display: flex;
    justify-content: center;
    margin-bottom: var(--spacing-lg);
}

.history-toggle-btn {
    background: linear-gradient(135deg, var(--focus-blue), var(--primary-green));
    color: var(--white);
    border: none;
    padding: var(--spacing-sm) var(--spacing-lg);
    border-radius: var(--radius-md);
    font-family: var(--font-primary);
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
}

.history-toggle-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(74, 144, 226, 0.3);
}

.history-section {
    animation: fadeInUp 0.6s ease-out;
}

.history-card {
    max-height: 400px;
    overflow-y: auto;
    scrollbar-width: thin;
    scrollbar-color: var(--focus-blue) var(--glass-bg);
}

.history-card::-webkit-scrollbar {
    width: 6px;
}

.history-card::-webkit-scrollbar-track {
    background: var(--glass-bg);
    border-radius: 3px;
}

.history-card::-webkit-scrollbar-thumb {
    background: var(--focus-blue);
    border-radius: 3px;
}

.history-card::-webkit-scrollbar-thumb:hover {
    background: var(--primary-green);
}

.history-list {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-sm);
}

.history-item {
    background: var(--glass-bg);
    backdrop-filter: blur(5px);
    -webkit-backdrop-filter: blur(5px);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-md);
    padding: var(--spacing-md);
    transition: all 0.3s ease;
    animation: fadeInUp 0.6s ease-out both;
    opacity: 0;
}

.history-item:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px var(--shadow-color);
    border-color: var(--focus-blue);
}

.history-word {
    font-family: var(--font-primary);
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--primary-green);
    margin-bottom: var(--spacing-xs);
}

.history-definition {
    font-size: 0.9rem;
    color: var(--text-dark);
    margin-bottom: var(--spacing-sm);
    line-height: 1.4;
}

.history-meta {
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 0.8rem;
    color: var(--text-dark);
    opacity: 0.7;
}

.history-time {
    font-style: italic;
}

.history-number {
    background: var(--focus-blue);
    color: var(--white);
    padding: 2px 6px;
    border-radius: 10px;
    font-size: 0.7rem;
    font-weight: 600;
}

.history-empty {
    text-align: center;
    padding: var(--spacing-xl);
    color: var(--text-dark);
    opacity: 0.7;
    font-style: italic;
}

/* Word Display Card */
.word-header {
    text-align: center;
    margin-bottom: var(--spacing-lg);
}

.word-header h3 {
    font-family: var(--font-primary);
    font-size: 1.3rem;
    font-weight: 600;
    color: var(--text-dark);
}

.word-content {
    text-align: center;
}

.word-title {
    font-family: var(--font-primary);
    font-size: 2.2rem;
    font-weight: 700;
    background: linear-gradient(135deg, var(--primary-green), var(--focus-blue));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: var(--spacing-md);
    min-height: 2.5rem;
    display: flex;
    align-items: center;
    justify-content: center;
    text-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
    animation: fadeInUp 0.6s ease-out;
}

.word-definition {
    font-size: 1.1rem;
    color: var(--text-dark);
    margin-bottom: var(--spacing-lg);
    line-height: 1.6;
    font-style: italic;
    min-height: 1.5rem;
    background: var(--glass-bg);
    backdrop-filter: blur(5px);
    -webkit-backdrop-filter: blur(5px);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    border: 1px solid var(--glass-border);
    animation: fadeInUp 0.6s ease-out 0.2s both;
}

.word-example {
    font-size: 0.95rem;
    color: var(--text-dark);
    opacity: 0.9;
    background: var(--glass-bg);
    backdrop-filter: blur(5px);
    -webkit-backdrop-filter: blur(5px);
    padding: var(--spacing-lg);
    border-radius: var(--radius-md);
    border-left: 4px solid var(--focus-blue);
    text-align: left;
    min-height: 3rem;
    display: flex;
    align-items: center;
    box-shadow: 0 2px 8px var(--shadow-color);
    animation: fadeInUp 0.6s ease-out 0.4s both;
}

@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.word-example:empty {
    display: none;
}

/* Notification Status */
.notification-status {
    background: linear-gradient(135deg, var(--focus-blue), var(--primary-green));
    color: var(--white);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    text-align: center;
    margin-top: var(--spacing-md);
}

.notification-info {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
}

.notification-icon {
    font-size: 1.2rem;
}

.notification-text {
    font-size: 0.9rem;
    font-weight: 500;
}

/* Footer */
.footer {
    text-align: center;
    padding: var(--spacing-lg) 0;
    margin-top: var(--spacing-xl);
    color: var(--text-dark);
    opacity: 0.6;
    font-size: 0.8rem;
}

/* Learning Active State */
.learning-active .logo {
    animation: pulse 2s ease-in-out infinite;
}

@keyframes pulse {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.05); }
}

/* Responsive Design */
@media (max-width: 768px) {
    .container {
        max-width: 100%;
        padding: var(--spacing-md);
    }

    .header-content {
        flex-direction: column;
        gap: var(--spacing-md);
        text-align: center;
    }

    .theme-toggle {
        align-self: flex-end;
    }

    .gamification-section {
        margin-top: var(--spacing-md);
        padding-top: var(--spacing-md);
    }

    .streak-display {
        flex-direction: column;
        text-align: center;
        gap: var(--spacing-sm);
    }

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

@media (max-width: 480px) {
    .container {
        padding: var(--spacing-sm);
    }

    .logo {
        font-size: 2rem;
    }

    .interval-grid {
        grid-template-columns: 1fr;
        gap: var(--spacing-sm);
    }

    .interval-btn {
        min-height: 70px;
        padding: var(--spacing-md);
    }

    .control-buttons {
        flex-direction: column;
    }

    .btn {
        min-width: 100%;
    }

    .status-item {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--spacing-xs);
    }

    .word-title {
        font-size: 1.5rem;
    }

    .gamification-section {
        margin-top: var(--spacing-sm);
        padding-top: var(--spacing-sm);
    }

    .streak-display {
        padding: var(--spacing-sm);
    }

    .progress-section {
        padding: var(--spacing-sm);
    }
}

@media (max-width: 360px) {
    .card {
        padding: var(--spacing-md);
    }

    .interval-time {
        font-size: 1.3rem;
    }

    .logo {
        font-size: 1.8rem;
    }

    .word-title {
        font-size: 1.3rem;
    }

    .streak-value {
        font-size: 1.2rem;
    }
}

/* Large screens */
@media (min-width: 1200px) {
    .container {
        max-width: 600px;
    }

    .logo {
        font-size: 3rem;
    }

    .card {
        padding: var(--spacing-xl);
    }

    .interval-grid {
        grid-template-columns: repeat(4, 1fr);
        gap: var(--spacing-lg);
    }

    .interval-btn {
        min-height: 90px;
        padding: var(--spacing-lg);
    }

    .word-title {
        font-size: 2.5rem;
    }
}

/* High contrast mode support */
@media (prefers-contrast: high) {
    :root {
        --shadow-color: rgba(0, 0, 0, 0.3);
        --shadow-hover: rgba(0, 0, 0, 0.4);
    }
    
    .card {
        border-width: 2px;
    }
    
    .interval-btn {
        border-width: 2px;
    }
}

/* Reduced motion support */
@media (prefers-reduced-motion: reduce) {
    * {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
    
    .learning-active .logo {
        animation: none;
    }
}