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

/* Page */
body{
    font-family: "Segoe UI", Arial, sans-serif;
    background:#f4f6f8;
    color:#1a1a1a;
    line-height:1.7;
}

/* Main container */
.container{
    max-width:900px;
    margin:auto;
    background:white;
    padding:50px;
}

/* Main title */
h1{
    font-size:40px;
    margin-bottom:15px;
}

/* Section titles */
h2{
    font-size:24px;
    margin-top:40px;
    margin-bottom:10px;
}

/* Paragraph spacing */
p{
    margin-bottom:16px;
}

/* Section divider */
section{
    margin-top:35px;
    padding-bottom:25px;
    border-bottom:1px solid #e6e6e6;
}

/* Subtopic blocks */
.subtopic{
    margin-top:25px;
}

.subtopic h3{
    font-size:20px;
    margin-bottom:6px;
}

/* Diagram */
.diagram{
    text-align:center;
    margin:25px 0;
}

.diagram img{
    max-width:100%;
}

.caption{
    font-size:14px;
    color:#666;
}

/* History box */
.history{
    background:#f7f7f7;
    padding:18px;
    border-left:4px solid #888;
}

/* Extras box */
.extras{
    background:#fafafa;
    padding:18px;
    border-left:4px solid #444;
}

/* Footer */
footer{
    margin-top:50px;
    text-align:center;
    font-size:14px;
    color:#777;
}