<hr> weird effect

HTML-CSS
#1

I started working on a tribute page and my hr element got this nice effect which I like, but not sure how or why it happened.
The bottom color is #bc6506 that I wrote in. The top color doesn’t appear in my code. Any thoughts?

here’s the code:

HTML:

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <link rel="stylesheet" href="./styles.css">
        <title>Sonny Rollins</title>
    </head>
    <body>
        <header>
            <h1>Sonny Rollins</h1>
            <p>The greatest living improviser.</p>
        </header>
        <hr>
        <main>
            <section class="introduction">
                <p>American jazz musician, a tenor saxophonist who was among the finest improvisers on the instrument to appear since the mid-1950s.</p>
            </section>
            <figure>
                <img src="./portrait.jpg" alt="Sonny Rollins preforming live" id="portrait">
                <figcaption>Sonny Rollins preforming live</figcaption>
            </figure>
            <section class="timeline">
                <ul>
                    <li>1930 - WALTER THEODORE ROLLINS was born in Harlem in NYC, and recievd his first saxophone at the age of 8.</li>
                    <li>1954 - The album Bags' Groove features his famous compositions: "Oleo", "Airegin", and "Doxy".</li>
                    <li>1956 - Saxophone Colossus, Rollins' sixth and widely acclaimed record, is released. He also records Tenor Madness with John Coltrane.\n Soon after, he goes on his first and most famous musical sabbatical.</li>
                    <li>1961 - Spending almost three years practicing daily, Sonny returns with his new album "The Bridge".</li>
                    <li>1969 - His second sabbatical. Before that Rollins explored different and varied musical styles.</li>
                    <li>1981 - Leaving the small nightclubs and turning to the large rock stages, he was also featured in three tracks by The Rolling Stones.</li>
                    <li>1997 - Was voted 'Jazz Artist of the Year' by Down Beat magazine. He releases his album "Global Warming".</li>
                    <li>2007 - He preformes at Carnegie Hall in commemoration of the fiftieth anniversary of his first performance there.</li>
                    <li>2017 - Donated his personal archive to the New York City Library.</li>
                </ul>
            </section>
        </main>
        <hr>
        <footer>
            <section class="sources">
                <a>https://www.britannica.com/biography/Sonny-Rollins</a>
                <a>https://sonnyrollins.com/</a>
                <a>https://en.wikipedia.org/wiki/Sonny_Rollins</a>
            </section>
        </footer>
    </body>
</html>

CSS

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

body {
    width: 100%;
    min-height: 100vh;
    color: white;
    background-color: #671706;
}

header {
    width: 100%;
}

hr {
    border-color: #bc6506;
    border-width: 1em;
    margin-top: 1em;
    margin-bottom: 1em;
}

main {
    width: 100%;
    display: flex;
    flex-flow: column;
    align-items: center;
}

#portrait {
    width: auto;
    height: 400px;
}

.timeline {
    margin: 3em;
}