:root {
    --bg-color: #f4f6f8;
    --panel-bg: #ffffff;
    --text-color: #2c3e50;
    --border-color: #bdc3c7;
    --primary: #3498db;
    --success: #2ecc71;
    --danger: #e74c3c;
    --header-bg: #34495e;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    margin: 0;
    padding: 20px;
}

h1 {
    text-align: center;
    color: var(--header-bg);
}

.tabs-nav {
    display: flex;
    gap: 10px;
    margin-bottom: 20px;
    justify-content: center;
}

.tab-btn {
    padding: 10px 20px;
    background: #e0e6ed;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-size: 1em;
    font-weight: bold;
}

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

.panel {
    background: var(--panel-bg);
    border-radius: 8px;
    padding: 20px;
    margin-bottom: 20px;
    box-shadow: 0 4px 6px rgba(0,0,0,0.05);
    border: 1px solid var(--border-color);
}

.upload-panel {
    text-align: center;
    padding: 40px 20px;
}

#midi-upload {
    font-size: 1.1em;
    padding: 20px;
    border: 2px dashed var(--primary);
    border-radius: 8px;
    cursor: pointer;
    width: 80%;
    max-width: 400px;
}

.transport-bar {
    display: flex;
    align-items: center;
    gap: 15px;
    padding: 15px;
    background: #fff;
    border-radius: 8px;
    margin-bottom: 20px;
    border: 1px solid var(--border-color);
}

.btn {
    padding: 10px 20px;
    border: none;
    border-radius: 4px;
    color: white;
    font-weight: bold;
    font-size: 1em;
    cursor: pointer;
}

.play-btn { background: var(--success); }
.stop-btn { background: var(--danger); }

#audio-status {
    font-weight: bold;
    color: #7f8c8d;
}

/* 4-Column Layout */
.registration-flex {
    display: flex;
    gap: 15px;
    overflow-x: auto;
    padding-top: 10px;
}

.division-col {
    flex: 1;
    min-width: 250px;
    background: #f8f9fa;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    overflow: hidden;
}

.division-col h4 {
    background: var(--header-bg);
    color: white;
    margin: 0;
    padding: 10px;
    text-align: center;
}

.stop-list {
    padding: 10px;
}

.stop-row {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 8px 0;
    border-bottom: 1px solid #ecf0f1;
}

.stop-row label {
    display: flex;
    align-items: center;
    gap: 8px;
    cursor: pointer;
    font-size: 0.9em;
}

.mapping-input {
    width: 60px;
    padding: 4px;
    text-align: center;
    border: 1px solid var(--border-color);
    border-radius: 4px;
}