:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --danger-color: #dc2626;
    --success-color: #16a34a;
    --warning-color: #d97706;
    --bg-color: #f3f4f6;
    --card-bg: #ffffff;
    --text-color: #1f2937;
    --text-muted: #6b7280;
    --border-color: #e5e7eb;
    --header-bg: #1e3a8a;
    --header-text: #ffffff;
}

@media (prefers-color-scheme: dark) {
    :root {
        --bg-color: #111827;
        --card-bg: #1f2937;
        --text-color: #f9fafb;
        --text-muted: #9ca3af;
        --border-color: #374151;
        --header-bg: #1e293b;
    }
}

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

body {
    font-family: system-ui, -apple-system, sans-serif;
    background: var(--bg-color);
    color: var(--text-color);
    line-height: 1.5;
    height: 100vh;
    overflow-y: hidden; /* App-like feel */
}

/* Constants Utilities */
.hidden { display: none !important; }
.text-center { text-align: center; }

/* Header */
.main-header {
    background: var(--header-bg);
    color: var(--header-text);
    padding: 1rem;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.header-content {
    max-width: 1200px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between; /* Space out title and user info */
    align-items: center;
}

#user-info {
    display: flex;
    gap: 1rem;
    align-items: center;
}

#callsign-display {
    font-weight: bold;
    background: rgba(255,255,255,0.1);
    padding: 0.25rem 0.75rem;
    border-radius: 4px;
}

/* Layout */
main {
    max-width: 1200px;
    margin: 0 auto;
    padding: 1rem;
    height: calc(100vh - 70px);
    overflow-y: auto;
}

.screen { display: none; }
.screen.active { display: block; animation: fadeIn 0.3s; }

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Buttons */
.btn {
    padding: 0.5rem 1rem;
    border: none;
    border-radius: 0.375rem;
    cursor: pointer;
    font-weight: 500;
    font-size: 0.9rem;
    transition: all 0.2s;
}

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

.btn-success { background: var(--success-color); color: white; }
.btn-success:hover { filter: brightness(90%); }

.btn-danger { background: var(--danger-color); color: white; }
.btn-danger:hover { filter: brightness(90%); }

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

.btn-outline {
    background: transparent;
    border: 1px solid currentColor;
    color: inherit;
}

.btn-block { width: 100%; display: block; }

/* Forms */
.form-group { margin-bottom: 1rem; }
.form-group label { display: block; margin-bottom: 0.25rem; font-size: 0.875rem; }
.form-group input, .form-group select {
    width: 100%;
    padding: 0.5rem;
    border: 1px solid var(--border-color);
    border-radius: 0.375rem;
    background: var(--card-bg);
    color: var(--text-color);
}
.form-row { display: flex; gap: 0.5rem; }
.form-row input { flex: 2; }
.form-row select { flex: 1; }

.error-msg { color: var(--danger-color); font-size: 0.875rem; margin-top: 0.5rem; }
.success-msg { color: var(--success-color); font-size: 0.875rem; margin-top: 0.5rem; }

/* Cards & Panels */
.card {
    background: var(--card-bg);
    border-radius: 0.5rem;
    box-shadow: 0 1px 3px rgba(0,0,0,0.1);
    border: 1px solid var(--border-color);
    overflow: hidden;
}

.card-header {
    padding: 1rem;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    justify-content: space-between;
    align-items: center;
    background: rgba(0,0,0,0.02);
}

.card-body { padding: 1rem; }

/* Auth Screen */
#auth-screen {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100%;
}
.auth-card {
    background: var(--card-bg);
    padding: 2rem;
    border-radius: 0.5rem;
    box-shadow: 0 4px 6px rgba(0,0,0,0.1);
    width: 100%;
    max-width: 400px;
    border: 1px solid var(--border-color);
}
.auth-card h2 { text-align: center; margin-bottom: 1.5rem; }

/* Dashboard Grid */
.dashboard-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: 1.5rem;
}
@media (min-width: 768px) {
    .dashboard-grid { grid-template-columns: 3fr 2fr; }
}

/* Frequencies List */
.frequencies-list-header {
    display: grid;
    grid-template-columns: 1fr 0.5fr 1fr 0.75fr 0.75fr;
    padding: 0.5rem;
    font-weight: bold;
    font-size: 0.875rem;
    color: var(--text-muted);
    border-bottom: 2px solid var(--border-color);
}
.frequency-item {
    display: grid;
    grid-template-columns: 1fr 0.5fr 1fr 0.75fr 0.75fr;
    padding: 0.75rem 0.5rem;
    border-bottom: 1px solid var(--border-color);
    align-items: center;
}
.frequency-item:last-child { border-bottom: none; }
.frequency-freq { font-weight: bold; color: var(--primary-color); }
.no-data { text-align: center; padding: 2rem; color: var(--text-muted); }

/* Tabs */
.tab-header { display: flex; gap: 0.5rem; padding-bottom: 0; }
.tab-btn {
    background: transparent;
    border: none;
    border-bottom: 2px solid transparent;
    padding: 0.75rem 1rem;
    cursor: pointer;
    color: var(--text-muted);
}
.tab-btn.active {
    border-bottom-color: var(--primary-color);
    color: var(--primary-color);
    font-weight: bold;
}
.tab-content { display: none; padding-top: 1rem; }
.tab-content.active { display: block; }

/* Upload Area */
.upload-area {
    border: 2px dashed var(--border-color);
    border-radius: 0.5rem;
    padding: 2rem;
    text-align: center;
    transition: all 0.2s;
}
.upload-area.dragover { border-color: var(--primary-color); background: rgba(37,99,235,0.05); }
.file-label {
    display: inline-block;
    margin-top: 0.5rem;
    padding: 0.5rem 1rem;
    background: var(--bg-color);
    border: 1px solid var(--border-color);
    border-radius: 0.375rem;
    cursor: pointer;
}

/* Admin Grid */
.admin-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: 2rem;
}
@media (min-width: 1024px) {
    .admin-grid { grid-template-columns: 1fr 2fr; }
}
.admin-panel h4 { margin-bottom: 1rem; border-bottom: 1px solid var(--border-color); padding-bottom: 0.5rem; }

/* Users Table */
.users-table { width: 100%; border-collapse: collapse; }
.users-table th, .users-table td { text-align: left; padding: 0.75rem; border-bottom: 1px solid var(--border-color); }
.users-table th { color: var(--text-muted); font-size: 0.875rem; }

/* Status online indicator pulse */
.status-indicator { color: var(--text-muted); transition: color 0.3s; }
.status-indicator.online { color: var(--success-color); animation: pulse 2s infinite; }
@keyframes pulse { 0% { opacity: 1; } 50% { opacity: 0.5; } 100% { opacity: 1; } }

/* Debug Console */
.debug-controls {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1rem;
    padding-bottom: 0.5rem;
    border-bottom: 1px solid var(--border-color);
}

.debug-status {
    font-size: 0.875rem;
    color: var(--text-muted);
}

.debug-logs {
    background: #1e1e1e;
    color: #d4d4d4;
    font-family: 'Monaco', 'Menlo', 'Courier New', monospace;
    font-size: 0.75rem;
    padding: 1rem;
    border-radius: 0.375rem;
    max-height: 600px;
    overflow-y: auto;
    line-height: 1.6;
}

.debug-line {
    padding: 0.25rem 0;
    border-bottom: 1px solid rgba(255,255,255,0.05);
}

.debug-error { color: #f48771; font-weight: bold; }
.debug-warning { color: #dcdcaa; }
.debug-info { color: #4ec9b0; }
.debug-debug { color: #9cdcfe; }

.btn-sm {
    padding: 0.25rem 0.75rem;
    font-size: 0.8rem;
}

/* Responsive tweaks */
@media (max-width: 640px) {
    .frequencies-list-header { display: none; }
    .frequency-item {
        grid-template-columns: 1fr 1fr;
        gap: 0.5rem;
    }
    .frequency-item > *:nth-child(n) { grid-column: auto; }
    .frequency-item button { grid-column: 2; grid-row: 1 / span 3; justify-self: end; }
    
    .debug-controls {
        flex-direction: column;
        align-items: flex-start;
        gap: 0.5rem;
    }
}