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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Helvetica Neue', Arial, sans-serif;
    background: var(--color-bg, #ffffff);
    color: var(--color-text, #000000);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: var(--spacing-md, 20px);
}

/* Layout Components */
.container {
    max-width: var(--container-max-width, 800px);
    width: 100%;
}

.container-sm {
    max-width: var(--container-sm-width, 600px);
    width: 100%;
}

/* Typography Components */
.heading {
    color: var(--color-text, #000000);
    text-align: center;
    margin-bottom: var(--spacing-sm, 15px);
    font-size: 2.5em;
    font-weight: 600;
    letter-spacing: -0.5px;
}

.heading-sm {
    font-size: 1.8em;
}

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

.text-muted {
    color: var(--color-text-muted, #666666);
}

/* Grid Components */
.grid {
    display: grid;
    gap: var(--spacing-md, 20px);
}

.grid-auto {
    grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
}

.grid-1 {
    grid-template-columns: 1fr;
}

/* Card Components */
.card {
    background: var(--color-bg, #ffffff);
    border: var(--border-width, 2px) solid var(--color-border, #000000);
    border-radius: var(--border-radius, 4px);
    padding: var(--spacing-lg, 30px);
    text-align: center;
    cursor: pointer;
    transition: all var(--transition-speed, 0.2s) ease;
}

.card:hover {
    border-width: calc(var(--border-width, 2px) + 1px);
}

.card-clickable {
    cursor: pointer;
}

.card-clickable:hover {
    background: var(--color-text, #000000);
    color: var(--color-bg, #ffffff);
}

.card-clickable:hover * {
    color: var(--color-bg, #ffffff);
}

.card-lg {
    padding: 50px;
    min-height: 400px;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    position: relative;
}

.card-title {
    color: var(--color-text, #000000);
    font-size: 1.8em;
    margin-bottom: var(--spacing-sm, 15px);
    font-weight: 600;
}

.card-icon {
    margin-bottom: var(--spacing-sm, 15px);
}

/* Icon Components */
.icon {
    display: inline-block;
    width: 48px;
    height: 48px;
    color: var(--color-text, #000000);
}

.icon-sm {
    width: 24px;
    height: 24px;
}

.icon-md {
    width: 32px;
    height: 32px;
}

.icon-lg {
    width: 64px;
    height: 64px;
}

.icon-xl {
    width: 80px;
    height: 80px;
}

.icon img,
.icon svg {
    width: 100%;
    height: 100%;
    display: block;
}

/* Button Components */
.btn {
    display: inline-block;
    padding: var(--spacing-sm, 10px) var(--spacing-md, 20px);
    border: var(--border-width, 2px) solid var(--color-border, #000000);
    border-radius: var(--border-radius, 4px);
    background: var(--color-bg, #ffffff);
    color: var(--color-text, #000000);
    text-decoration: none;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-speed, 0.2s) ease;
}

.btn:hover {
    background: var(--color-text, #000000);
    color: var(--color-bg, #ffffff);
}

.btn-primary {
    background: var(--color-text, #000000);
    color: var(--color-bg, #ffffff);
}

.btn-primary:hover {
    background: var(--color-text-hover, #333333);
}

.btn-lg {
    padding: var(--spacing-sm, 15px) var(--spacing-lg, 40px);
    font-size: 1.1em;
    font-weight: 600;
}

/* Spacing Components */
.mb-sm {
    margin-bottom: var(--spacing-sm, 15px);
}

.mb-md {
    margin-bottom: var(--spacing-md, 20px);
}

.mb-lg {
    margin-bottom: var(--spacing-lg, 30px);
}

/* Flip Card Component */
.flip-card.show-back .flip-front {
    display: none;
}

.flip-card.show-back .flip-back {
    display: block;
}

.flip-front, .flip-back {
    width: 100%;
    text-align: center;
}

.flip-back {
    display: none;
}

/* Content Components */
.content-primary {
    font-size: 3em;
    color: var(--color-text, #000000);
    font-weight: 600;
    margin-bottom: var(--spacing-md, 20px);
    letter-spacing: -1px;
}

.content-label {
    font-size: 1.2em;
    color: var(--color-text-muted, #666666);
    font-style: italic;
    padding: 8px 20px;
    margin-bottom: var(--spacing-lg, 25px);
    border: 1px solid var(--color-border, #000000);
    border-radius: var(--border-radius, 4px);
    display: inline-block;
}

.content-body {
    font-size: 1.4em;
    color: var(--color-text, #000000);
    margin-bottom: var(--spacing-lg, 25px);
    line-height: 1.6;
    font-weight: 500;
}

.content-quote {
    font-size: 1.1em;
    color: var(--color-text-muted, #666666);
    font-style: italic;
    line-height: 1.6;
    padding: var(--spacing-md, 20px);
    border-left: 3px solid var(--color-border, #000000);
}

.content-hint {
    position: absolute;
    bottom: var(--spacing-md, 20px);
    font-size: 0.9em;
    color: var(--color-text-light, #999999);
}

/* Flexbox Components */
.flex {
    display: flex;
}

.flex-center {
    justify-content: center;
    align-items: center;
}

.flex-gap {
    gap: var(--spacing-sm, 15px);
}

/* Settings Components */
.settings-btn {
    position: fixed;
    top: var(--spacing-md, 20px);
    right: var(--spacing-md, 20px);
    width: 50px;
    height: 50px;
    border: var(--border-width, 2px) solid var(--color-border, #000000);
    border-radius: var(--border-radius, 4px);
    background: var(--color-bg, #ffffff);
    color: var(--color-text, #000000);
    cursor: pointer;
    transition: all var(--transition-speed, 0.2s) ease;
    z-index: 1000;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 10px;
}

.settings-btn:hover {
    background: var(--color-text, #000000);
    color: var(--color-bg, #ffffff);
}

/* Mastered Words Button (Top Left) */
.mastered-btn {
    position: fixed;
    top: var(--spacing-md, 20px);
    left: var(--spacing-md, 20px);
    width: 50px;
    height: 50px;
    border: var(--border-width, 2px) solid var(--color-border, #000000);
    border-radius: 50%;
    background: var(--color-bg, #ffffff);
    color: var(--color-text, #000000);
    cursor: pointer;
    transition: all var(--transition-speed, 0.2s) ease;
    z-index: 1000;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 600;
    font-size: 1.2em;
}

.mastered-btn:hover {
    background: var(--color-text, #000000);
    color: var(--color-bg, #ffffff);
}

/* Mastered Words List */
.mastered-list {
    max-height: 400px;
    overflow-y: auto;
    padding: var(--spacing-sm, 10px) 0;
}

.mastered-card {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-md, 15px);
    margin-bottom: var(--spacing-sm, 10px);
    background: var(--color-bg, #ffffff);
    border: var(--border-width, 2px) solid var(--color-border, #000000);
    border-radius: var(--border-radius, 4px);
    transition: all var(--transition-speed, 0.2s) ease;
}

.mastered-card:hover {
    background: #f9f9f9;
}

.mastered-word {
    font-size: 1.1em;
    font-weight: 500;
    color: var(--color-text, #000000);
}

.btn-sm {
    padding: 8px 16px;
    font-size: 0.85em;
}

.settings-modal {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.5);
    z-index: 2000;
    align-items: center;
    justify-content: center;
}

.settings-modal.active {
    display: flex;
}

.settings-content {
    background: var(--color-bg, #ffffff);
    border: var(--border-width, 2px) solid var(--color-border, #000000);
    border-radius: var(--border-radius, 4px);
    padding: var(--spacing-lg, 30px);
    max-width: 400px;
    width: 90%;
    position: relative;
}

.settings-header {
    font-size: 1.5em;
    font-weight: 600;
    margin-bottom: var(--spacing-lg, 30px);
    color: var(--color-text, #000000);
}

.settings-close {
    position: absolute;
    top: var(--spacing-sm, 10px);
    right: var(--spacing-sm, 10px);
    width: 30px;
    height: 30px;
    border: none;
    background: transparent;
    color: var(--color-text, #000000);
    cursor: pointer;
    padding: 0;
    display: flex;
    align-items: center;
    justify-content: center;
}

.settings-close:hover {
    opacity: 0.7;
}

.settings-option {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-md, 20px) 0;
    border-bottom: 1px solid var(--color-border, #000000);
}

.settings-option:last-child {
    border-bottom: none;
}

.settings-label {
    font-size: 1.1em;
    font-weight: 500;
    color: var(--color-text, #000000);
}

.settings-description {
    font-size: 0.85em;
    color: var(--color-muted, #666666);
    margin-top: var(--spacing-xs, 5px);
    line-height: 1.4;
}

.settings-divider {
    height: 1px;
    background: var(--color-border, #000000);
    margin: var(--spacing-md, 20px) 0;
}

.settings-buttons {
    display: flex;
    gap: var(--spacing-sm, 10px);
    padding: var(--spacing-md, 20px) 0;
}

.settings-buttons .btn {
    flex: 1;
}

/* Text Input Component */
.text-input {
    width: 100%;
    padding: var(--spacing-sm, 12px) var(--spacing-md, 15px);
    font-size: 1em;
    border: var(--border-width, 2px) solid var(--color-border, #000000);
    border-radius: var(--border-radius, 4px);
    background: var(--color-bg, #ffffff);
    color: var(--color-text, #000000);
    font-family: inherit;
    outline: none;
    transition: border-color var(--transition-speed, 0.2s) ease;
}

.text-input:focus {
    border-color: var(--color-text, #000000);
}

.text-input::placeholder {
    color: var(--color-muted, #666666);
    opacity: 0.7;
}

/* Toggle Switch Component */
.toggle-switch {
    position: relative;
    width: 120px;
    height: 40px;
    background: var(--color-bg, #ffffff);
    border: var(--border-width, 2px) solid var(--color-border, #000000);
    border-radius: var(--border-radius, 4px);
    cursor: pointer;
    display: flex;
    align-items: center;
    overflow: hidden;
}

.toggle-option {
    flex: 1;
    text-align: center;
    font-size: 0.85em;
    font-weight: 600;
    z-index: 2;
    transition: color var(--transition-speed, 0.2s) ease;
    color: var(--color-text, #000000);
}

.toggle-slider {
    position: absolute;
    width: 50%;
    height: calc(100% - 4px);
    background: var(--color-text, #000000);
    border-radius: 2px;
    top: 2px;
    left: 2px;
    transition: transform var(--transition-speed, 0.2s) ease;
    z-index: 1;
}

.toggle-switch[data-value="dark"] .toggle-slider {
    transform: translateX(100%);
}

.toggle-switch[data-value="default"] .toggle-option:first-child,
.toggle-switch[data-value="dark"] .toggle-option:last-child {
    color: var(--color-bg, #ffffff);
}

/* Responsive Utilities */
@media (max-width: 768px) {
    :root {
        --spacing-sm: 10px;
        --spacing-md: 15px;
        --spacing-lg: 25px;
    }

    body {
        align-items: flex-start;
        padding-top: var(--spacing-md, 20px);
    }

    .heading {
        font-size: 1.8em;
    }

    .grid-auto {
        grid-template-columns: 1fr;
    }

    .card {
        padding: 25px;
    }

    .card-lg {
        padding: 30px 20px;
        min-height: 350px;
    }

    .card-title {
        font-size: 1.5em;
    }

    .card-icon {
        font-size: 2.5em;
    }

    .content-primary {
        font-size: 2em;
    }

    .content-label {
        font-size: 1em;
        padding: 6px 15px;
    }

    .content-body {
        font-size: 1.1em;
    }

    .content-quote {
        font-size: 1em;
        padding: var(--spacing-sm, 15px);
    }

    .content-hint {
        font-size: 0.8em;
    }

    .btn {
        padding: 8px 16px;
        font-size: 0.95em;
    }

    .btn-lg {
        padding: 12px 30px;
        font-size: 1em;
    }
}

@media (max-width: 480px) {
    :root {
        --spacing-sm: 8px;
        --spacing-md: 10px;
        --spacing-lg: 20px;
    }

    .heading {
        font-size: 1.5em;
    }

    .card {
        padding: 20px;
    }

    .card-lg {
        padding: 25px 15px;
        min-height: 300px;
    }

    .card-title {
        font-size: 1.3em;
    }

    .card-icon {
        font-size: 2em;
    }

    .content-primary {
        font-size: 1.6em;
    }

    .content-label {
        font-size: 0.9em;
    }

    .content-body {
        font-size: 1em;
    }

    .content-quote {
        font-size: 0.95em;
        padding: 12px;
    }
}