sub-menu에 백그라운드 색상을 화이트로 넣어도 뒤에 보더가 ... - 인프런

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <link rel="stylesheet" href="/레이아웃css/11_상단드롭다운1.css" />
  </head>
  <body>
    <div class="container">
      <div class="header-container">
        <header>
          <div class="header-logo"></div>
          <div class="header-navi">
            <ul class="menu">
              <li>
                <a href="#none">Menu1</a>
                <div class="subMenu">
                  <a href="#none">Sub-Menu-1</a>
                  <a href="#none">Sub-Menu-2</a>
                  <a href="#none">Sub-Menu-3</a>
                  <a href="#none">Sub-Menu-4</a>
                </div>
              </li>
              <li>
                <a href="#none">Menu2</a>
                <div class="subMenu">
                  <a href="#none">Sub-Menu-1</a>
                  <a href="#none">Sub-Menu-2</a>
                  <a href="#none">Sub-Menu-3</a>
                  <a href="#none">Sub-Menu-4</a>
                </div>
              </li>
              <li>
                <a href="#none">Menu3</a>
                <div class="subMenu">
                  <a href="#none">Sub-Menu-1</a>
                  <a href="#none">Sub-Menu-2</a>
                  <a href="#none">Sub-Menu-3</a>
                  <a href="#none">Sub-Menu-4</a>
                </div>
              </li>
              <li>
                <a href="#none">Menu4</a>
                <div class="subMenu">
                  <a href="#none">Sub-Menu-1</a>
                  <a href="#none">Sub-Menu-2</a>
                  <a href="#none">Sub-Menu-3</a>
                  <a href="#none">Sub-Menu-4</a>
                </div>
              </li>
            </ul>
          </div>
        </header>
      </div>
      <div class="content-container">
        <div class="slide">
          <div></div>
        </div>
        <div class="items">
          <div class="gallery"></div>
          <div class="banner"></div>
          <div class="barogo"></div>
        </div>
      </div>
      <div class="footer-container">
        <footer>
          <div class="footer-logo"></div>
          <div class="footer-navi-copyright"></div>
        </footer>
      </div>
    </div>
  </body>
</html>
body {
  margin: 0;
}
.header-container {
  border: 1px solid black;
  display: flex;
  justify-content: center;
}
header {
  border: 1px solid black;
  width: 1200px;
  display: flex;
  justify-content: space-between;
}
header > div {
  border: 1px solid black;
  height: 100px;
}
.header-logo {
  width: 200px;
}
.header-navi {
  width: 600px;
}
.content-container {
  display: flex;
  flex-direction: column;
  align-items: center;
}
.slide {
  width: 1200px;
  border: 1px solid black;
}
.slide > div {
  height: 300px;
}
.items {
  width: 1200px;
  display: flex;
  border: 1px solid black;
}
.items > div {
  border: 1px solid black;
  height: 200px;
  flex: 1;
}
.footer-container {
  border: 1px solid black;
  display: flex;
  justify-content: center;
}
footer {
  width: 1200px;
  display: flex;
}
footer > div {
  border: 1px solid black;
  height: 100px;
}
.footer-logo {
  width: 200px;
}
a {
  text-decoration: none;
  color: black;
}
.footer-navi-copyright {
  width: 1000px;
}
/* Navigation */
.menu {
  list-style: none;
  padding: 0;
}
.menu > li {
  text-align: center;
  width: 150px;
  float: left;
  box-sizing: border-box;
}
.menu > li > a {
  border: 1px solid black;
  display: block;
}
.menu > li > .subMenu > a {
  display: block;
  padding: 5px;
}
.subMenu {
  border: 1px solid black;
  background-color: white;
}
코드 상황은 이러한데 네비게이션 뒤로 자꾸 보더가 보이는데 이걸 어떻게 해결할 수 있을까요 ..?
인프런 커뮤니티 질문&답변

sub-menu에 백그라운드 색상을 화이트로 넣어도 뒤에 보더가 보여요.
