:root {
    /* Colors from spec */
    --color-primary: #0D9488;
    --color-secondary: #0F766E;
    --color-accent: #B45309;
    --color-background: #F0FDFA;
    --color-surface: #FFFFFF;
    --color-text: #134E4A;
    --color-text-secondary: #5F9EA0;
    --color-success: #10B981;
    --color-error: #EF4444;

    /* Typography */
    --font-primary: 'IBM Plex Sans', system-ui, -apple-system, sans-serif;
    --font-secondary: 'IBM Plex Serif', Georgia, serif;

    /* Spacing - normal scale */
    --spacing-xs: 0.5rem;
    --spacing-sm: 0.75rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;

    /* Border radius - Standardized */
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;

    /* Shadows */
    --shadow-sm: 0 1px 3px rgba(13, 148, 136, 0.1);
    --shadow-md: 0 4px 12px rgba(13, 148, 136, 0.12);
    --shadow-lg: 0 8px 24px rgba(13, 148, 136, 0.15);

    /* Animation - subtle */
    --transition-fast: 200ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-base: 300ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 400ms cubic-bezier(0.4, 0, 0.2, 1);
}

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

body {
    font-family: var(--font-primary);
    line-height: 1.6;
    color: var(--color-text);
    background-color: var(--color-background);
    -webkit-font-smoothing: antialiased;
    overflow-x: hidden;
}

/* Skip Link (Accessibility) */
.skip-link {
    position: absolute;
    top: -40px;
    left: 0;
    background: var(--color-primary, #4A7C8C);
    color: #fff;
    padding: 8px 16px;
    text-decoration: none;
    z-index: 1000;
    border-radius: 0 0 4px 0;
}

.skip-link:focus {
    top: 0;
}

.back-to-catalog {
    position: fixed;
    top: 1rem;
    left: 1rem;
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.5rem 1rem;
    font-size: 0.875rem;
    font-weight: 500;
    color: #4A7C8C;
    background: rgba(255, 255, 255, 0.95);
    border: 1px solid #E8E4DD;
    border-radius: 6px;
    text-decoration: none;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
    z-index: 1000;
    transition: all 0.2s ease;
}

.back-to-catalog:hover {
    background: #4A7C8C;
    color: white;
    border-color: #4A7C8C;
}

.back-to-catalog:focus {
    outline: 2px solid #4A7C8C;
    outline-offset: 2px;
}

/* Booking Container */
.booking-container {
    display: flex;
    min-height: 100vh;
    position: relative;
}

/* Course List */
.course-list {
    flex: 1;
    padding: var(--spacing-xl);
    max-width: 1200px;
    margin: 0 auto;
    transition: margin-right var(--transition-slow);
}

.course-list.sidebar-open {
    margin-right: 420px;
}

.course-list__header {
    margin-bottom: var(--spacing-xl);
}

.course-list__title {
    font-size: 2rem;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: var(--spacing-sm);
    letter-spacing: -0.02em;
}

.course-list__subtitle {
    font-size: 1.125rem;
    color: var(--color-text-secondary);
    font-weight: 400;
}

/* Course Grid */
.course-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: var(--spacing-lg);
}

/* Course Card */
.course-card {
    background: var(--color-surface);
    border-radius: var(--radius-lg);
    overflow: hidden;
    box-shadow: var(--shadow-sm);
    cursor: pointer;
    transition: all var(--transition-base);
    border: 2px solid transparent;
}

.course-card:hover {
    box-shadow: var(--shadow-md);
    transform: translateY(-2px);
    border-color: var(--color-primary);
}

.course-card:focus-visible {
    outline: 3px solid var(--color-primary);
    outline-offset: 2px;
}

.course-card__image {
    width: 100%;
    height: 160px;
    overflow: hidden;
    background: var(--color-primary);
}

.course-card__image img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    display: block;
}

.course-card__content {
    padding: var(--spacing-lg);
}

.course-card__title {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--color-text);
    margin-bottom: var(--spacing-sm);
    line-height: 1.3;
}

.course-card__instructor {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
    font-size: 0.9375rem;
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-md);
}

.course-card__meta {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-md);
    font-size: 0.875rem;
    color: var(--color-text-secondary);
}

.course-card__meta > span {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
}

.course-card__price {
    font-weight: 600;
    color: var(--color-text);
}

.icon {
    opacity: 0.7;
}

/* Availability Bar */
.course-card__availability {
    margin-top: var(--spacing-md);
}

.availability-bar {
    height: 6px;
    background: #E0F2F1;
    border-radius: var(--radius-sm);
    overflow: hidden;
    margin-bottom: var(--spacing-xs);
}

.availability-bar__fill {
    height: 100%;
    background: var(--color-success);
    transition: width var(--transition-base);
}

.availability-bar--low .availability-bar__fill {
    background: var(--color-accent);
}

.availability-text {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
}

.availability-text--urgent {
    color: var(--color-accent);
    font-weight: 500;
}

/* Sidebar */
.sidebar {
    position: fixed;
    top: 0;
    right: 0;
    width: 420px;
    height: 100vh;
    background: var(--color-surface);
    box-shadow: -4px 0 24px rgba(13, 148, 136, 0.15);
    transform: translateX(100%);
    transition: transform var(--transition-slow);
    z-index: 1000;
    overflow-y: auto;
}

.sidebar.open {
    transform: translateX(0);
}

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

.sidebar__close {
    position: absolute;
    top: var(--spacing-lg);
    right: var(--spacing-lg);
    background: transparent;
    border: none;
    cursor: pointer;
    color: var(--color-text-secondary);
    padding: var(--spacing-xs);
    border-radius: var(--radius-sm);
    transition: all var(--transition-fast);
}

.sidebar__close:hover {
    background: var(--color-background);
    color: var(--color-text);
}

.sidebar__close:focus-visible {
    outline: 2px solid var(--color-primary);
    outline-offset: 2px;
}

.sidebar__header {
    margin-bottom: var(--spacing-lg);
    padding-right: var(--spacing-xl);
}

.sidebar__title {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--color-text);
    margin-bottom: var(--spacing-xs);
    line-height: 1.3;
}

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

.sidebar__details {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-lg);
    padding: var(--spacing-lg);
    background: var(--color-background);
    border-radius: var(--radius-md);
}

.detail-item {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xs);
}

.detail-item__label {
    font-size: 0.8125rem;
    color: var(--color-text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    font-weight: 500;
}

.detail-item__value {
    font-size: 0.9375rem;
    color: var(--color-text);
    font-weight: 500;
}

/* Accordion */
.accordion {
    margin-bottom: var(--spacing-xl);
    border: 1px solid #B2DFDB;
    border-radius: var(--radius-md);
    overflow: hidden;
}

.accordion__trigger {
    width: 100%;
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: var(--spacing-md);
    background: var(--color-surface);
    border: none;
    cursor: pointer;
    font-family: var(--font-primary);
    font-size: 0.9375rem;
    font-weight: 500;
    color: var(--color-primary);
    transition: background var(--transition-fast);
}

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

.accordion__trigger:focus-visible {
    outline: 2px solid var(--color-primary);
    outline-offset: -2px;
}

.accordion__icon {
    transition: transform var(--transition-base);
}

.accordion__trigger[aria-expanded="true"] .accordion__icon {
    transform: rotate(180deg);
}

.accordion__content {
    max-height: 0;
    overflow: hidden;
    transition: max-height var(--transition-slow);
}

.accordion__content[aria-hidden="false"] {
    max-height: 800px;
}

.accordion__body {
    padding: var(--spacing-lg);
    background: var(--color-background);
}

.accordion__heading {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--color-text);
    margin-bottom: var(--spacing-sm);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.accordion__list {
    list-style: none;
    margin-bottom: var(--spacing-lg);
}

.accordion__list li {
    padding-left: var(--spacing-lg);
    position: relative;
    margin-bottom: var(--spacing-xs);
    color: var(--color-text);
    font-size: 0.9375rem;
}

.accordion__list li::before {
    content: '•';
    position: absolute;
    left: var(--spacing-sm);
    color: var(--color-primary);
    font-weight: bold;
}

.accordion__text {
    color: var(--color-text);
    font-size: 0.9375rem;
    margin-bottom: var(--spacing-lg);
}

.accordion__text:last-child {
    margin-bottom: 0;
}

/* Booking Form */
.booking-form {
    background: var(--color-surface);
}

.booking-form__title {
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--color-text);
    margin-bottom: var(--spacing-lg);
    padding-bottom: var(--spacing-md);
    border-bottom: 2px solid var(--color-primary);
}

.form-group {
    margin-bottom: var(--spacing-lg);
}

.form-label {
    display: block;
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--color-text);
    margin-bottom: var(--spacing-xs);
}

.required {
    color: var(--color-error);
}

.optional {
    color: var(--color-text-secondary);
    font-weight: 400;
}

.form-input {
    width: 100%;
    padding: var(--spacing-sm) var(--spacing-md);
    font-family: var(--font-primary);
    font-size: 0.9375rem;
    color: var(--color-text);
    background: var(--color-background);
    border: 2px solid #B2DFDB;
    border-radius: var(--radius-sm);
    transition: all var(--transition-fast);
}

.form-input:hover {
    border-color: var(--color-primary);
}

.form-input:focus {
    outline: none;
    border-color: var(--color-primary);
    background: var(--color-surface);
    box-shadow: 0 0 0 3px rgba(13, 148, 136, 0.1);
}

.form-input.error {
    border-color: var(--color-error);
}

.form-input.error:focus {
    box-shadow: 0 0 0 3px rgba(239, 68, 68, 0.1);
}

.form-input.success {
    border-color: var(--color-success, #10B981);
}

.form-input.success:focus {
    box-shadow: 0 0 0 3px rgba(16, 185, 129, 0.1);
}

.form-group {
    position: relative;
}

.form-group.has-error .form-input {
    border-color: var(--color-error);
}

.form-group.has-success .form-input {
    border-color: var(--color-success, #10B981);
}

.form-group.has-success::after {
    content: '✓';
    position: absolute;
    right: var(--spacing-md);
    top: 2.5rem;
    transform: translateY(50%);
    color: var(--color-success, #10B981);
    font-weight: 700;
    font-size: 1.25rem;
    pointer-events: none;
}

.form-error {
    display: block;
    font-size: 0.8125rem;
    color: var(--color-error);
    margin-top: var(--spacing-xs);
    min-height: 1.2em;
}

.form-submit {
    width: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-md) var(--spacing-lg);
    font-family: var(--font-primary);
    font-size: 1rem;
    font-weight: 600;
    color: var(--color-surface);
    background: var(--color-primary);
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-base);
}

.form-submit:hover {
    background: var(--color-secondary);
    box-shadow: var(--shadow-md);
    transform: translateY(-1px);
}

.form-submit:active {
    transform: translateY(0);
}

.form-submit:focus-visible {
    outline: 3px solid var(--color-primary);
    outline-offset: 2px;
}

.form-submit__icon {
    transition: transform var(--transition-fast);
}

.form-submit:hover .form-submit__icon {
    transform: translateX(4px);
}

/* Modal */
.modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 2000;
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 0;
    pointer-events: none;
    transition: opacity var(--transition-base);
}

.modal.open {
    opacity: 1;
    pointer-events: auto;
}

.modal__overlay {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(13, 148, 136, 0.4);
    backdrop-filter: blur(4px);
}

.modal__content {
    position: relative;
    background: var(--color-surface);
    border-radius: var(--radius-lg);
    padding: var(--spacing-2xl);
    max-width: 500px;
    width: 90%;
    box-shadow: var(--shadow-lg);
    transform: scale(0.9);
    transition: transform var(--transition-base);
    text-align: center;
}

.modal.open .modal__content {
    transform: scale(1);
}

.modal__close {
    position: absolute;
    top: var(--spacing-lg);
    right: var(--spacing-lg);
    background: transparent;
    border: none;
    cursor: pointer;
    color: var(--color-text-secondary);
    padding: var(--spacing-xs);
    border-radius: var(--radius-sm);
    transition: all var(--transition-fast);
}

.modal__close:hover {
    background: var(--color-background);
    color: var(--color-text);
}

.modal__close:focus-visible {
    outline: 2px solid var(--color-primary);
    outline-offset: 2px;
}

.modal__icon {
    margin: 0 auto var(--spacing-lg);
    animation: scaleIn var(--transition-slow) cubic-bezier(0.34, 1.56, 0.64, 1);
}

@keyframes scaleIn {
    from {
        transform: scale(0);
        opacity: 0;
    }
    to {
        transform: scale(1);
        opacity: 1;
    }
}

.modal__title {
    font-size: 1.75rem;
    font-weight: 600;
    color: var(--color-text);
    margin-bottom: var(--spacing-sm);
}

.modal__message {
    font-size: 1rem;
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-xl);
}

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

.modal__action {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-md) var(--spacing-lg);
    font-family: var(--font-primary);
    font-size: 0.9375rem;
    font-weight: 500;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-fast);
    border: none;
}

.modal__action--primary {
    background: var(--color-primary);
    color: var(--color-surface);
}

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

.modal__action--secondary {
    background: var(--color-background);
    color: var(--color-primary);
}

.modal__action--secondary:hover {
    background: #B2DFDB;
}

.modal__action--link {
    background: transparent;
    color: var(--color-text-secondary);
    font-size: 0.875rem;
    text-decoration: underline;
    padding: 0.5rem 1rem;
}

.modal__action--link:hover {
    background: transparent;
    color: var(--color-primary);
}

.modal__action:focus-visible {
    outline: 2px solid var(--color-primary);
    outline-offset: 2px;
}

.modal__action-icon {
    opacity: 0.8;
}

/* Reduced Motion */
@media (prefers-reduced-motion: reduce) {
    * {
        animation-duration: 0.01ms !important;
        transition-duration: 0.01ms !important;
    }
}

/* Responsive */
@media (max-width: 768px) {
    .course-list {
        padding: var(--spacing-lg);
    }

    .course-list.sidebar-open {
        margin-right: 0;
    }

    .course-list__title {
        font-size: 1.75rem;
    }

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

    .sidebar {
        width: 100%;
    }

    .sidebar__content {
        padding: var(--spacing-lg);
    }

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

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