:root {
    /* Color Palette - Modern & Refined */
    --color-primary: #2563eb;
    --color-primary-dark: #1d4ed8;
    --color-primary-light: #dbeafe;
    --color-secondary: #64748b;
    --color-background: #f8fafc;
    --color-surface: #ffffff;
    --color-text-main: #0f172a;
    --color-text-muted: #64748b;
    --color-border: #e2e8f0;
    --color-error: #ef4444;
    --color-success: #10b981;

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

    /* Typography */
    --font-sans: 'Noto Sans JP', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-brand: 'Outfit', sans-serif;

    /* Border Radius */
    --radius-sm: 6px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-full: 9999px;

    /* Shadows */
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
}

/* Reset */
*,
*::before,
*::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    -webkit-text-size-adjust: 100%;
    -webkit-tap-highlight-color: transparent;
}

body {
    font-family: var(--font-sans);
    background-color: var(--color-background);
    color: var(--color-text-main);
    line-height: 1.7;
    font-size: 16px;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
    min-height: 100dvh;
}

a {
    text-decoration: none;
    color: inherit;
    transition: color 0.2s, opacity 0.2s;
}

a:hover {
    opacity: 0.8;
}

ul {
    list-style: none;
}

img {
    max-width: 100%;
    height: auto;
}

/* ===== Layout ===== */
.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

/* ===== Header ===== */
.site-header {
    position: sticky;
    top: 0;
    z-index: 100;
    background-color: var(--color-surface);
    border-bottom: 1px solid var(--color-border);
    padding: var(--spacing-sm) 0;
}

.header-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    min-height: 48px;
    gap: var(--spacing-sm);
}

.brand-logo {
    font-family: var(--font-brand);
    font-size: 1rem;
    font-weight: 600;
    color: var(--color-primary);
    letter-spacing: -0.02em;
    white-space: nowrap;
    flex-shrink: 0;
}

@media (min-width: 480px) {
    .brand-logo {
        font-size: 1.25rem;
    }
}

.main-nav {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
}

.nav-link {
    font-size: 0.8125rem;
    color: var(--color-text-muted);
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: var(--radius-sm);
    transition: background-color 0.2s, color 0.2s;
    min-height: 40px;
    display: inline-flex;
    align-items: center;
    white-space: nowrap;
}

@media (min-width: 480px) {
    .nav-link {
        font-size: 0.875rem;
        padding: var(--spacing-sm) var(--spacing-md);
        min-height: 44px;
    }
}

.nav-link:hover {
    color: var(--color-primary);
    background-color: var(--color-primary-light);
}

.user-greeting {
    font-size: 0.8125rem;
    color: var(--color-text-muted);
    white-space: nowrap;
}

@media (min-width: 480px) {
    .user-greeting {
        font-size: 0.875rem;
    }
}

/* ===== Buttons ===== */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--radius-sm);
    font-weight: 500;
    font-size: 0.9375rem;
    cursor: pointer;
    border: none;
    transition: all 0.2s;
    min-height: 44px;
    gap: var(--spacing-xs);
    white-space: nowrap;
}

.btn-primary {
    background-color: var(--color-primary);
    color: white;
}

.btn-primary:hover {
    background-color: var(--color-primary-dark);
    opacity: 1;
}

.btn-outline {
    background-color: transparent;
    color: var(--color-primary);
    border: 1.5px solid var(--color-primary);
}

.btn-outline:hover {
    background-color: var(--color-primary-light);
    opacity: 1;
}

.btn-ghost {
    background-color: transparent;
    color: var(--color-text-muted);
}

.btn-ghost:hover {
    background-color: var(--color-background);
    color: var(--color-text-main);
}

.btn-lg {
    padding: var(--spacing-md) var(--spacing-lg);
    font-size: 1rem;
    min-height: 52px;
}

.btn-sm {
    padding: var(--spacing-xs) var(--spacing-sm);
    font-size: 0.875rem;
    min-height: 36px;
}

.btn-full {
    width: 100%;
}

.btn-text {
    color: var(--color-primary);
    font-weight: 500;
    font-size: 0.9375rem;
    padding: var(--spacing-xs);
    min-height: 44px;
    display: inline-flex;
    align-items: center;
}

/* ===== Forms ===== */
.form-group {
    display: block;
    margin-bottom: var(--spacing-md);
}

.form-label {
    display: block;
    margin-bottom: var(--spacing-xs);
    font-weight: 500;
    font-size: 0.9375rem;
    color: var(--color-text-main);
}

.form-input,
.form-group input[type="text"],
.form-group input[type="password"],
.form-group input[type="email"],
.form-group input[type="number"],
.form-group input[type="tel"],
.form-group input[type="url"],
.form-group input[type="search"],
.form-group input[type="date"],
.form-group input[type="time"],
.form-group select,
.form-group textarea {
    display: block;
    width: 100%;
    max-width: 100%;
    padding: var(--spacing-sm) var(--spacing-md);
    border: 1.5px solid var(--color-border);
    border-radius: var(--radius-sm);
    font-size: 1rem;
    font-family: inherit;
    background-color: var(--color-surface);
    color: var(--color-text-main);
    min-height: 48px;
    transition: border-color 0.2s, box-shadow 0.2s;
    -webkit-appearance: none;
    appearance: none;
    box-sizing: border-box;
}

.form-input:focus,
.form-group input:focus,
.form-group select:focus,
.form-group textarea:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: 0 0 0 3px var(--color-primary-light);
}

.form-input::placeholder {
    color: var(--color-text-muted);
}

/* ===== Cards ===== */
.card {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    overflow: hidden;
    transition: border-color 0.2s, box-shadow 0.2s;
}

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

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

.card-footer {
    padding: var(--spacing-md);
    background-color: var(--color-background);
    border-top: 1px solid var(--color-border);
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 0.875rem;
}

/* ===== Sections ===== */
.section {
    margin-bottom: var(--spacing-xl);
}

.section-title {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: var(--spacing-md);
    color: var(--color-text-main);
}

.page-title {
    font-size: 1.5rem;
    font-weight: 700;
    line-height: 1.3;
}

@media (min-width: 640px) {
    .page-title {
        font-size: 2rem;
    }
}

/* ===== Page Header ===== */
.page-header {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-lg);
    padding-bottom: var(--spacing-md);
    border-bottom: 1px solid var(--color-border);
}

@media (min-width: 640px) {
    .page-header {
        flex-direction: row;
        justify-content: space-between;
        align-items: center;
    }
}

.back-link {
    display: inline-flex;
    align-items: center;
    font-size: 0.875rem;
    color: var(--color-text-muted);
    margin-bottom: var(--spacing-xs);
}

/* ===== Dashboard ===== */
.dashboard-header {
    display: flex;
    flex-direction: row;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-lg);
    align-items: center;
}

.card-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--spacing-md);
}

@media (min-width: 640px) {
    .card-grid {
        grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    }
}

.group-name {
    font-size: 1.125rem;
    font-weight: 600;
    margin-bottom: var(--spacing-xs);
}

.group-desc {
    color: var(--color-text-muted);
    font-size: 0.875rem;
    line-height: 1.5;
}

/* ===== Auth Pages ===== */
.auth-container {
    display: flex;
    justify-content: center;
    padding: var(--spacing-lg) var(--spacing-md);
}

.auth-card {
    background: var(--color-surface);
    padding: var(--spacing-lg);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    width: 100%;
    max-width: 400px;
    box-shadow: var(--shadow-sm);
}

.auth-title {
    text-align: center;
    margin-bottom: var(--spacing-lg);
    font-size: 1.5rem;
    font-weight: 600;
}

.auth-footer {
    margin-top: var(--spacing-lg);
    text-align: center;
    font-size: 0.9375rem;
    color: var(--color-text-muted);
}

.auth-footer a {
    color: var(--color-primary);
    font-weight: 500;
}

/* ===== Error States ===== */
.error-list {
    color: var(--color-error);
    font-size: 0.875rem;
    margin-top: var(--spacing-xs);
}

.error-summary {
    background-color: #fef2f2;
    border: 1px solid var(--color-error);
    border-radius: var(--radius-sm);
    color: #b91c1c;
    padding: var(--spacing-md);
    margin-bottom: var(--spacing-md);
    font-size: 0.9375rem;
}

.help-text {
    font-size: 0.8125rem;
    color: var(--color-text-muted);
    margin-top: var(--spacing-xs);
    line-height: 1.5;
}

/* ===== Hero Section ===== */
.hero-section {
    padding: var(--spacing-xl) 0;
    background-color: var(--color-background);
}

.hero-container {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xl);
}

@media (min-width: 768px) {
    .hero-container {
        display: grid;
        grid-template-columns: 1fr 1fr;
        align-items: center;
        min-height: 70vh;
    }
}

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

@media (min-width: 768px) {
    .hero-content {
        text-align: left;
    }
}

.hero-title {
    font-family: var(--font-brand);
    font-size: 2.5rem;
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: var(--spacing-md);
    color: var(--color-text-main);
}

@media (min-width: 768px) {
    .hero-title {
        font-size: 3.5rem;
    }
}

.hero-subtitle {
    font-size: 1rem;
    color: var(--color-text-muted);
    margin-bottom: var(--spacing-lg);
    line-height: 1.8;
}

@media (min-width: 768px) {
    .hero-subtitle {
        font-size: 1.125rem;
    }
}

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

@media (min-width: 480px) {
    .hero-actions {
        flex-direction: row;
        justify-content: center;
    }
}

@media (min-width: 768px) {
    .hero-actions {
        justify-content: flex-start;
    }
}

.hero-image {
    display: none;
}

@media (min-width: 768px) {
    .hero-image {
        display: block;
    }
}

/* ===== Member List ===== */
.member-list {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-sm);
}

.member-item {
    background: var(--color-background);
    border: 1px solid var(--color-border);
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--radius-sm);
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    font-size: 0.875rem;
}

.badge {
    background: var(--color-border);
    color: var(--color-secondary);
    font-size: 0.75rem;
    padding: 2px 8px;
    border-radius: var(--radius-full);
    text-transform: uppercase;
    font-weight: 500;
}

/* ===== Invite Section ===== */
.invite-section {
    background: var(--color-primary-light);
    padding: var(--spacing-lg);
    border-radius: var(--radius-md);
    border: 1px solid #bae6fd;
    margin-bottom: var(--spacing-xl);
}

.invite-grid {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

@media (min-width: 768px) {
    .invite-grid {
        display: grid;
        grid-template-columns: 1fr 1fr;
    }
}

.invite-method h3 {
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: var(--spacing-sm);
}

.invite-input-group {
    display: flex;
    gap: var(--spacing-sm);
}

.invite-input-group input {
    flex: 1;
    min-width: 0;
}

.invite-note {
    font-size: 0.8125rem;
    color: var(--color-text-muted);
    margin-top: var(--spacing-xs);
}

/* ===== Grid (Heatmap) ===== */
.grid-container {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    overflow: hidden;
    margin-bottom: var(--spacing-lg);
}

.grid-wrapper {
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
}

.grid-table {
    display: inline-block;
    min-width: 100%;
}

.grid-row {
    display: flex;
}

.grid-cell {
    width: 40px;
    height: 32px;
    border-right: 1px solid var(--color-background);
    border-bottom: 1px solid var(--color-background);
    flex-shrink: 0;
    display: flex;
    align-items: center;
    justify-content: center;
}

.header-row {
    position: sticky;
    top: 0;
    z-index: 10;
    background: var(--color-background);
}

.time-header {
    width: 44px;
    background: var(--color-background);
    position: sticky;
    left: 0;
    z-index: 20;
    border-right: 1px solid var(--color-border);
}

.date-header {
    flex-direction: column;
    height: 44px;
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--color-text-main);
}

.day-name {
    color: var(--color-text-muted);
    font-weight: 400;
    font-size: 0.6875rem;
}

.time-label {
    width: 44px;
    font-size: 0.6875rem;
    color: var(--color-text-muted);
    background: var(--color-surface);
    position: sticky;
    left: 0;
    z-index: 15;
    border-right: 1px solid var(--color-background);
    justify-content: flex-end;
    padding-right: 4px;
}

.slot-cell {
    background: var(--color-surface);
    transition: background 0.1s;
}

/* Heatmap Colors */
.cell-0 {
    background-color: var(--color-surface);
}

.cell-low {
    background-color: #bfdbfe;
}

.cell-mid {
    background-color: #60a5fa;
}

.cell-high {
    background-color: #2563eb;
}

.cell-100 {
    background-color: #1e40af;
}

/* ===== Time Range Form ===== */
.time-range-form {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    flex-wrap: wrap;
}

.time-range-form label {
    font-size: 0.875rem;
    color: var(--color-text-muted);
}

.time-range-form select {
    padding: var(--spacing-xs) var(--spacing-sm);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    font-size: 0.875rem;
    min-height: 36px;
    background: var(--color-surface);
}

/* ===== Main Content ===== */
.main-content {
    flex: 1;
    padding: var(--spacing-lg) 0;
}

/* ===== Footer ===== */
.site-footer {
    background-color: var(--color-surface);
    border-top: 1px solid var(--color-border);
    padding: var(--spacing-lg) 0;
    text-align: center;
    color: var(--color-text-muted);
    font-size: 0.8125rem;
}

/* ===== Empty State ===== */
.empty-state {
    text-align: center;
    padding: var(--spacing-xl);
    background: var(--color-background);
    border-radius: var(--radius-md);
}

.empty-state p {
    color: var(--color-text-muted);
    margin-bottom: var(--spacing-md);
}

/* ===== Utilities ===== */
.text-muted {
    color: var(--color-text-muted);
}

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

.text-sm {
    font-size: 0.875rem;
}

.flex {
    display: flex;
}

.flex-between {
    justify-content: space-between;
}

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

.flex-wrap {
    flex-wrap: wrap;
}

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

.gap-sm {
    gap: var(--spacing-sm);
}

.gap-md {
    gap: var(--spacing-md);
}

.mb-sm {
    margin-bottom: var(--spacing-sm);
}

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

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

.hidden {
    display: none;
}

@media (min-width: 640px) {
    .sm\:block {
        display: block;
    }

    .sm\:flex {
        display: flex;
    }
}

/* Header Actions */
.header-actions {
    display: flex;
    gap: 10px;
    flex-wrap: wrap;
}

@media (max-width: 640px) {
    .header-actions {
        width: 100%;
    }

    .header-actions .btn {
        flex: 1;
        text-align: center;
    }
}

/* Event List */
.event-list {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.event-card {
    display: flex;
    align-items: center;
    gap: 16px;
    padding: 16px;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    transition: box-shadow 0.2s;
}

.event-card:hover {
    box-shadow: var(--shadow-md);
}

.event-date {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-width: 60px;
    padding: 8px;
    background: var(--color-primary-light);
    border-radius: var(--radius-sm);
}

.event-day {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--color-primary);
}

.event-weekday {
    font-size: 0.75rem;
    color: var(--color-primary);
    opacity: 0.8;
}

.event-info {
    flex: 1;
}

.event-title {
    font-weight: 600;
    font-size: 1rem;
    color: var(--color-text-main);
    margin-bottom: 2px;
}

.event-time {
    font-size: 0.85rem;
    color: var(--color-text-muted);
}

/* Delete Button */
.btn-delete {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 36px;
    height: 36px;
    border: 1px solid var(--color-border);
    background: var(--color-background);
    color: var(--color-text-muted);
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 1.25rem;
    transition: all 0.2s;
    flex-shrink: 0;
}

.btn-delete:hover {
    background: var(--color-error);
    color: #fff;
    border-color: var(--color-error);
}

.event-delete-form {
    margin-left: auto;
}

/* Secondary Button */
.btn-secondary {
    background: var(--color-surface);
    color: var(--color-text-main);
    border: 1px solid var(--color-border);
}

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

/* Tooltip Styles */
.grid-tooltip {
    display: none;
    position: fixed;
    background: rgba(15, 23, 42, 0.95);
    color: #fff;
    padding: 6px 10px;
    border-radius: 4px;
    font-size: 0.75rem;
    white-space: nowrap;
    z-index: 9999;
    pointer-events: none;
    box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    border: 1px solid rgba(255, 255, 255, 0.1);
}