Borda no cabeçalho | CSS: dispondo elementos com Flexbox e Grid

Depois de colocar a cor no background do cabeçalho ficam essas bordas: Borda cabeçalho

Meu código

<!DOCTYPE html>
<html lang="pt-br">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title> HZC | Home </title>
    <link rel="preconnect" href="https://fonts.googleapis.com">
    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
    <link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=Open+Sans:wght@400;600;700&display=swap">
    <link rel="stylesheet" href=.assets/css/reset.css">
    <link rel="stylesheet" href="./assets/css/body.css">
    <link rel="stylesheet" href="./assets/css/cabecalho/cabecalho.css">
    <link rel="stylesheet" href="./assets/css/cabecalho/cabecalho-menu.css">
    <link rel="stylesheet" href="./assets/css/cabecalho/cabecalho-logo.css">
    <link rel="stylesheet" href="./assets/css/cabecalho/cabecalho-notificacoes.css">
</head>
<body>
    <header class="cabecalho">
        <button class="cabecalho__menu">menu</button>
        <img class="cabecalho__logo" src="./assets/img/logo.svg" alt="Logotipo HZC">
        <button class="cabecalho__notificacoes">notificações</button>
    </header>
</body>
</html>

.cabecalho {
    display: flex;
    justify-content: space-between;
    align-items: center;
    background-color: #15191c;
    padding: 8px 16px;
    box-shadow: 0px 4px 4px rgba(0, 0, 0, 0.16);
}

.cabecalho__notificacoes {
    background-color: transparent;
    border: none;
    color: #FFFFFF;
    margin-top: 1.5rem;
}

.cabecalho__menu {
    background-color: transparent;
    border: none;
    color: #FFFFFF;
    margin-top: 1.5rem;
}

.cabecalho__logo {
    height: 3rem;
}

Ps: Resolvido, aparentemente o reset.css não estava funcionando, apaguei e reescrevi a tag link e ficou normal.