:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --danger-color: #dc2626;
    --danger-hover: #b91c1c;
    --success-color: #16a34a;
    --border-color: #e5e7eb;
    --bg-gray: #f9fafb;
    --text-gray: #6b7280;
    --text-dark: #1f2937;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Hiragino Sans', 'Hiragino Kaku Gothic ProN', Meiryo, sans-serif;
    line-height: 1.6;
    color: var(--text-dark);
    background: var(--bg-gray);
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px;
}

/* Header */
header {
    background: white;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
    padding: 20px 0;
    margin-bottom: 30px;
}

header h1 {
    font-size: 24px;
    color: var(--primary-color);
    margin-bottom: 5px;
}

header .conference-date {
    color: var(--text-gray);
    font-size: 14px;
}

/* Buttons */
.btn {
    display: inline-block;
    padding: 10px 20px;
    border: none;
    border-radius: 6px;
    cursor: pointer;
    font-size: 14px;
    font-weight: 500;
    text-decoration: none;
    transition: all 0.2s;
}

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

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

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

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

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

.btn-secondary {
    background: var(--text-gray);
    color: white;
}

.btn-small {
    padding: 6px 12px;
    font-size: 12px;
}

/* Forms */
.form-group {
    margin-bottom: 20px;
}

.form-group label {
    display: block;
    margin-bottom: 5px;
    font-weight: 500;
    color: var(--text-dark);
}

.form-group input,
.form-group textarea,
.form-group select {
    width: 100%;
    padding: 10px;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    font-size: 14px;
    font-family: inherit;
}

.form-group textarea {
    min-height: 100px;
    resize: vertical;
}

/* Cards */
.card {
    background: white;
    border-radius: 8px;
    padding: 20px;
    margin-bottom: 20px;
    box-shadow: 0 1px 3px rgba(0,0,0,0.1);
}

.card h2 {
    font-size: 20px;
    margin-bottom: 15px;
    color: var(--text-dark);
}

/* Dashboard specific */
.dashboard-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
}

.presentation-list {
    margin-top: 20px;
}

.presentation-item {
    background: var(--bg-gray);
    padding: 15px;
    border-radius: 6px;
    margin-bottom: 10px;
    display: flex;
    justify-content: space-between;
    align-items: start;
}

.presentation-info {
    flex: 1;
}

.presentation-info h3 {
    font-size: 16px;
    margin-bottom: 5px;
}

.presentation-meta {
    font-size: 13px;
    color: var(--text-gray);
    margin-bottom: 3px;
}

.presentation-actions {
    display: flex;
    gap: 10px;
}

/* Login */
.login-container {
    max-width: 400px;
    margin: 100px auto;
    padding: 40px;
    background: white;
    border-radius: 8px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

.login-container h1 {
    text-align: center;
    margin-bottom: 30px;
    color: var(--primary-color);
}

/* Timetable */
.controls {
    display: flex;
    gap: 15px;
    margin-bottom: 20px;
    flex-wrap: wrap;
}

.search-box {
    flex: 1;
    min-width: 200px;
}

.search-box input {
    width: 100%;
    padding: 10px;
    border: 1px solid var(--border-color);
    border-radius: 6px;
}

.sort-buttons {
    display: flex;
    gap: 10px;
}

.timetable-container {
    overflow-x: auto;
}

.timetable {
    width: 100%;
    border-collapse: collapse;
    background: white;
    min-width: 600px;
}

.timetable th,
.timetable td {
    border: 1px solid var(--border-color);
    padding: 12px;
    text-align: left;
}

.timetable th {
    background: var(--primary-color);
    color: white;
    font-weight: 500;
    position: sticky;
    top: 0;
    z-index: 10;
}

.presentation-card {
    background: var(--bg-gray);
    padding: 12px;
    border-radius: 6px;
    margin-bottom: 10px;
}

.presentation-card:last-child {
    margin-bottom: 0;
}

.presentation-title {
    font-weight: 500;
    margin-bottom: 5px;
    color: var(--text-dark);
}

.presentation-presenter {
    font-size: 13px;
    color: var(--text-gray);
    margin-bottom: 8px;
}

.presentation-card-actions {
    display: flex;
    gap: 8px;
    flex-wrap: wrap;
}

/* List view */
.presentation-list-view {
    display: grid;
    gap: 15px;
}

.presentation-list-card {
    background: white;
    padding: 20px;
    border-radius: 8px;
    box-shadow: 0 1px 3px rgba(0,0,0,0.1);
}

.presentation-list-card h3 {
    font-size: 18px;
    margin-bottom: 10px;
    color: var(--text-dark);
}

.presentation-details {
    display: grid;
    gap: 8px;
    margin-bottom: 12px;
}

.presentation-detail {
    font-size: 14px;
    color: var(--text-gray);
}

.presentation-detail strong {
    color: var(--text-dark);
    font-weight: 500;
}

/* Selection */
.select-checkbox {
    margin-right: 10px;
}

.bulk-actions {
    position: sticky;
    bottom: 20px;
    background: white;
    padding: 15px;
    border-radius: 8px;
    box-shadow: 0 4px 12px rgba(0,0,0,0.15);
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-top: 20px;
}

/* Modal */
.modal {
    display: none;
    position: fixed;
    z-index: 1000;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background: rgba(0,0,0,0.5);
    overflow: auto;
}

.modal.active {
    display: block;
}

.modal-content {
    background: white;
    margin: 50px auto;
    padding: 30px;
    border-radius: 8px;
    max-width: 600px;
    position: relative;
}

.modal-close {
    position: absolute;
    right: 15px;
    top: 15px;
    font-size: 28px;
    font-weight: bold;
    color: var(--text-gray);
    cursor: pointer;
    line-height: 1;
}

.modal-close:hover {
    color: var(--text-dark);
}

.modal h2 {
    margin-bottom: 20px;
}

/* Alert */
.alert {
    padding: 12px 20px;
    border-radius: 6px;
    margin-bottom: 20px;
}

.alert-success {
    background: #d1fae5;
    color: #065f46;
    border: 1px solid #6ee7b7;
}

.alert-error {
    background: #fee2e2;
    color: #991b1b;
    border: 1px solid #fca5a5;
}

/* Responsive */
@media (max-width: 768px) {
    .container {
        padding: 10px;
    }
    
    header h1 {
        font-size: 20px;
    }
    
    .controls {
        flex-direction: column;
    }
    
    .search-box {
        width: 100%;
    }
    
    .dashboard-header {
        flex-direction: column;
        align-items: flex-start;
        gap: 10px;
    }
    
    .presentation-item {
        flex-direction: column;
        gap: 10px;
    }
    
    .presentation-actions {
        width: 100%;
    }
    
    .presentation-actions button {
        flex: 1;
    }
    
    .bulk-actions {
        flex-direction: column;
        gap: 10px;
        align-items: stretch;
    }
    
    .modal-content {
        margin: 20px;
        padding: 20px;
    }
}

/* Loading */
.loading {
    text-align: center;
    padding: 40px;
    color: var(--text-gray);
}

/* Empty state */
.empty-state {
    text-align: center;
    padding: 60px 20px;
    color: var(--text-gray);
}

.empty-state h3 {
    font-size: 18px;
    margin-bottom: 10px;
}