/* Custom Fonts & Global Reset */
:root {
    /* Color Palette - Light Theme Default */
    --bg-gradient-start: #f8fafc;
    --bg-gradient-end: #e2e8f0;
    --card-bg: rgba(255, 255, 255, 0.85);
    --card-border: rgba(226, 232, 240, 0.8);
    --text-primary: #0f172a;
    --text-secondary: #475569;
    --accent: #2563eb;
    --accent-hover: #1d4ed8;
    --accent-light: rgba(37, 99, 235, 0.1);
    --progress-bg: #e2e8f0;
    --progress-fill: linear-gradient(90deg, #2563eb, #3b82f6);
    --shadow-color: rgba(15, 23, 42, 0.08);
    --btn-secondary-bg: #ffffff;
    --btn-secondary-border: #cbd5e1;
    --btn-secondary-text: #334155;
    --btn-secondary-hover: #f1f5f9;
    --nav-link-color: #64748b;
    --nav-link-hover: #0f172a;
    
    --font-sans: 'Outfit', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    --font-display: 'Space Grotesk', sans-serif;
    
    --transition-speed: 0.3s;
}

[data-theme="dark"] {
    /* Color Palette - Dark Theme */
    --bg-gradient-start: #0f172a;
    --bg-gradient-end: #020617;
    --card-bg: rgba(30, 41, 59, 0.7);
    --card-border: rgba(255, 255, 255, 0.08);
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    --accent: #3b82f6;
    --accent-hover: #60a5fa;
    --accent-light: rgba(96, 165, 250, 0.15);
    --progress-bg: #1e293b;
    --progress-fill: linear-gradient(90deg, #3b82f6, #60a5fa);
    --shadow-color: rgba(0, 0, 0, 0.4);
    --btn-secondary-bg: #1e293b;
    --btn-secondary-border: #334155;
    --btn-secondary-text: #cbd5e1;
    --btn-secondary-hover: #334155;
    --nav-link-color: #94a3b8;
    --nav-link-hover: #f8fafc;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: var(--font-sans);
    background: linear-gradient(135deg, var(--bg-gradient-start), var(--bg-gradient-end));
    color: var(--text-primary);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: space-between;
    transition: background var(--transition-speed) ease, color var(--transition-speed) ease;
    padding: 1.5rem;
}

/* Header & Navigation */
.app-header {
    width: 100%;
    max-width: 600px;
    text-align: center;
    margin-bottom: 2rem;
}

.top-nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1.5rem;
}

.edward-link {
    font-size: 0.85rem;
    color: var(--nav-link-color);
    text-decoration: underline;
    font-weight: 500;
    transition: color var(--transition-speed);
}

.edward-link:hover {
    color: var(--nav-link-hover);
    text-decoration: underline;
}

.theme-toggle {
    background: none;
    border: none;
    cursor: pointer;
    color: var(--text-secondary);
    padding: 0.5rem;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: background-color var(--transition-speed), color var(--transition-speed);
}

.theme-toggle:hover {
    background-color: var(--accent-light);
    color: var(--accent);
}

.theme-toggle .icon {
    width: 1.25rem;
    height: 1.25rem;
}

/* Toggle icon display based on theme */
[data-theme="dark"] .moon-icon {
    display: none;
}
:not([data-theme="dark"]) .sun-icon {
    display: none;
}

.main-title {
    font-family: var(--font-display);
    font-weight: 800;
    font-size: 2.25rem;
    letter-spacing: -0.025em;
    margin-bottom: 0.5rem;
}

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

/* Main Area Layout */
.app-main {
    flex: 1;
    width: 100%;
    max-width: 600px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 1.5rem;
}

/* Progress Indicator */
.progress-container {
    width: 100%;
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.progress-bar {
    width: 100%;
    height: 6px;
    background-color: var(--progress-bg);
    border-radius: 9999px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background: var(--progress-fill);
    border-radius: 9999px;
    transition: width var(--transition-speed) cubic-bezier(0.4, 0, 0.2, 1);
}

.progress-text {
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--text-secondary);
    align-self: flex-end;
}

/* Flashcard Styles with 3D Flip */
.flashcard-wrapper {
    width: 100%;
    height: 320px;
    perspective: 1200px;
    cursor: pointer;
}

.flashcard {
    width: 100%;
    height: 100%;
    position: relative;
    transform-style: preserve-3d;
    transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
    border-radius: 24px;
    outline: none;
}

.flashcard:focus-visible {
    box-shadow: 0 0 0 3px var(--accent);
}

.flashcard.is-flipped {
    transform: rotateY(180deg);
}

.card-face {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: 24px;
    border: 1px solid var(--card-border);
    background: var(--card-bg);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    box-shadow: 0 10px 25px -5px var(--shadow-color), 0 8px 10px -6px var(--shadow-color);
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    align-items: center;
    padding: 1.75rem;
    text-align: center;
}

.card-reverse {
    transform: rotateY(180deg);
}

.card-side-label {
    font-size: 0.75rem;
    font-weight: 800;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--accent);
    background-color: var(--accent-light);
    padding: 0.25rem 0.75rem;
    border-radius: 9999px;
}

.card-content {
    font-family: var(--font-display);
    font-size: 1.85rem;
    font-weight: 600;
    line-height: 1.3;
    padding: 0 1rem;
    word-break: keep-all;
    overflow-wrap: break-word;
}

.tap-hint {
    font-size: 0.8rem;
    color: var(--text-secondary);
    opacity: 0.7;
    transition: opacity var(--transition-speed);
}

.flashcard:hover .tap-hint {
    opacity: 1;
}

/* Audio button custom style */
.audio-action-container {
    margin-top: auto;
    margin-bottom: auto;
    width: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
}

.audio-link {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    background-color: var(--accent);
    color: #ffffff;
    text-decoration: none;
    padding: 0.75rem 1.25rem;
    border-radius: 12px;
    font-weight: 600;
    font-size: 0.95rem;
    transition: background-color var(--transition-speed), transform 0.2s ease, box-shadow var(--transition-speed);
    box-shadow: 0 4px 6px -1px var(--shadow-color);
}

.audio-link:hover {
    background-color: var(--accent-hover);
    transform: translateY(-2px);
    box-shadow: 0 8px 12px -2px var(--shadow-color);
}

.audio-link:active {
    transform: translateY(0);
}

.speaker-icon {
    width: 1.25rem;
    height: 1.25rem;
}

/* Controls */
.controls {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 1rem;
    width: 100%;
}

.btn {
    font-family: var(--font-sans);
    font-size: 1rem;
    font-weight: 600;
    border-radius: 14px;
    border: none;
    cursor: pointer;
    transition: all var(--transition-speed) ease;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
}

.btn-primary {
    background-color: var(--accent);
    color: #ffffff;
    padding: 1rem 2.5rem;
    box-shadow: 0 4px 6px -1px var(--shadow-color);
}

.btn-primary:hover {
    background-color: var(--accent-hover);
    transform: translateY(-1px);
}

.btn-secondary {
    background-color: var(--btn-secondary-bg);
    border: 1px solid var(--btn-secondary-border);
    color: var(--btn-secondary-text);
    padding: 0.85rem 1.5rem;
}

.btn-secondary:hover {
    background-color: var(--btn-secondary-hover);
}

.btn-text {
    background: none;
    border: none;
    color: var(--text-secondary);
    padding: 0.5rem 1rem;
    font-size: 0.85rem;
    gap: 0.25rem;
}

.btn-text:hover {
    color: var(--accent);
    background-color: var(--accent-light);
}

.utilities {
    display: flex;
    justify-content: center;
    gap: 1.5rem;
    width: 100%;
    margin-top: 0.5rem;
}

/* Footer styling */
.app-footer {
    width: 100%;
    text-align: center;
    margin-top: 3rem;
    font-size: 0.8rem;
    color: var(--text-secondary);
    opacity: 0.8;
}

/* Known toggle styling */
.known-toggle {
    position: absolute;
    top: 1.25rem;
    right: 1.25rem;
    width: 2.25rem;
    height: 2.25rem;
    border-radius: 50%;
    border: 2px solid var(--btn-secondary-border);
    background-color: var(--btn-secondary-bg);
    color: var(--text-secondary);
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: all var(--transition-speed) ease;
    padding: 0;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.05);
    z-index: 10;
}

.known-toggle svg {
    width: 1.15rem;
    height: 1.15rem;
    opacity: 0.3;
    transition: opacity var(--transition-speed), transform var(--transition-speed);
}

@media (hover: hover) {
    .known-toggle:hover {
        border-color: #10b981;
        color: #10b981;
    }

    .known-toggle:hover svg {
        opacity: 0.8;
        transform: scale(1.1);
    }
}

/* Active known state */
.flashcard.is-known .known-toggle {
    background-color: #10b981;
    border-color: #10b981;
    color: #ffffff;
    box-shadow: 0 4px 10px rgba(16, 185, 129, 0.3);
}

.flashcard.is-known .known-toggle svg {
    opacity: 1;
}


/* Responsiveness adjustments */
@media (max-width: 480px) {
    body {
        padding: 1rem;
    }
    
    .main-title {
        font-size: 1.85rem;
    }
    
    .flashcard-wrapper {
        height: 280px;
    }
    
    .card-content {
        font-size: 1.45rem;
    }
    
    .btn-primary {
        padding: 0.85rem 1.75rem;
    }
    
    .btn-secondary {
        padding: 0.75rem 1.15rem;
    }
}