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

body {
    font-family: 'Segoe UI', Arial, sans-serif;
    background: linear-gradient(135deg, #f5f7fa 0%, #e4e8ec 100%);
    min-height: 100vh;
    padding: 15px;
}

main {
    max-width: 900px;
    margin: 0 auto;
}

.title {
    text-align: center;
    font-size: 22px;
    color: #2c3e50;
    margin-bottom: 15px;
    font-weight: 600;
}

.subtitle {
    text-align: center;
    font-size: 13px;
    color: #666;
    margin-bottom: 20px;
}

.container {
    display: flex;
    gap: 15px;
    justify-content: center;
    flex-wrap: wrap;
}

.branch {
    flex: 1;
    min-width: 280px;
    max-width: 400px;
}

.branch-title {
    text-align: center;
    padding: 12px;
    border-radius: 10px;
    font-weight: 600;
    font-size: 15px;
    margin-bottom: 12px;
    cursor: pointer;
    transition: transform 0.2s, box-shadow 0.2s;
}

.branch-title:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(0,0,0,0.15);
}

.addition-branch .branch-title {
    background: linear-gradient(135deg, #3498db 0%, #2980b9 100%);
    color: white;
}

.scalar-branch .branch-title {
    background: linear-gradient(135deg, #27ae60 0%, #1e8449 100%);
    color: white;
}

.axiom-card {
    background: white;
    border-radius: 10px;
    padding: 12px;
    margin-bottom: 10px;
    cursor: pointer;
    transition: all 0.3s ease;
    border-left: 4px solid transparent;
    box-shadow: 0 2px 4px rgba(0,0,0,0.05);
}

.axiom-card:hover {
    transform: translateX(5px);
    box-shadow: 0 4px 12px rgba(0,0,0,0.1);
}

.addition-branch .axiom-card {
    border-left-color: #3498db;
}

.scalar-branch .axiom-card {
    border-left-color: #27ae60;
}

.axiom-card.viewed {
    background: #f8fffe;
}

.axiom-card.viewed::after {
    content: '\2713';
    float: right;
    color: #27ae60;
    font-weight: bold;
}

.axiom-name {
    font-weight: 600;
    font-size: 14px;
    color: #2c3e50;
    margin-bottom: 4px;
}

.axiom-formula {
    font-family: 'Times New Roman', serif;
    font-style: italic;
    color: #555;
    font-size: 14px;
}

.axiom-details {
    display: none;
    margin-top: 10px;
    padding-top: 10px;
    border-top: 1px solid #eee;
}

.axiom-card.expanded .axiom-details {
    display: block;
}

.axiom-description {
    font-size: 13px;
    color: #666;
    line-height: 1.5;
    margin-bottom: 8px;
}

.axiom-example {
    background: #f8f9fa;
    padding: 10px;
    border-radius: 6px;
    font-size: 12px;
    color: #555;
}

.axiom-example strong {
    color: #2c3e50;
}

.center-hub {
    text-align: center;
    margin: 20px 0;
}

.hub-node {
    display: inline-block;
    background: linear-gradient(135deg, #9b59b6 0%, #8e44ad 100%);
    color: white;
    padding: 15px 25px;
    border-radius: 50px;
    font-weight: 600;
    font-size: 16px;
    cursor: pointer;
    transition: all 0.3s;
    position: relative;
}

.hub-node:hover {
    transform: scale(1.05);
    box-shadow: 0 6px 20px rgba(155, 89, 182, 0.4);
}

.hub-tooltip {
    display: none;
    position: absolute;
    background: white;
    color: #333;
    padding: 12px;
    border-radius: 8px;
    box-shadow: 0 4px 15px rgba(0,0,0,0.2);
    width: 280px;
    top: 100%;
    left: 50%;
    transform: translateX(-50%);
    margin-top: 10px;
    font-weight: normal;
    font-size: 13px;
    text-align: left;
    z-index: 100;
}

.hub-node:hover .hub-tooltip {
    display: block;
}

.progress-bar {
    text-align: center;
    margin-top: 15px;
    font-size: 13px;
    color: #666;
}

.progress-fill {
    display: inline-block;
    background: #27ae60;
    color: white;
    padding: 4px 12px;
    border-radius: 15px;
    font-size: 12px;
}

@media (max-width: 700px) {
    .branch {
        min-width: 100%;
    }
}