将边框添加到作为边框构建的三角形

Question

我正在尝试在下拉列表左上角的三角形中添加红色边框。但问题是三角形本身是边界。所以我不知道该怎么做。请帮帮我。

＆＃13;

＆＃13;

.dropdown {
  position: relative;
  vertical-align: middle;
  display: inline-block;
}

.dropdown-content {
  position: absolute;
  min-width: 160px;
  background-color: yellow;
  padding: 12px 16px;
  margin-top: 20px;
  z-index: 1;
  border-color: red;
 border-width: thin;
 border-style: solid;
}

.dropdown-content a{
  display: block;
}

.dropdown-content:after {
    position: absolute;
    left: 70%;
    top: -20px;
    width: 0;
    height: 0;
    content: '';
	border-left: 20px solid transparent;
    border-right: 20px solid transparent;
    border-bottom: 20px solid yellow;
}

＆＃13;

<div class='dropdown'>
  <div class="dropdown-content">
    <a href="#">Link 1</a>
    <a href="#">Link 2</a>
    <a href="#">Link 3</a>
  </div>
</div>

＆＃13;

＆＃13;

＆＃13;

Answer 1

您可以使用另一个伪元素添加三角形边框。

.dropdown-content:before,
.dropdown-content:after {
  position: absolute;
  left: 70%;
  width: 0;
  height: 0;
  content: '';
  border-left: 20px solid transparent;
  border-right: 20px solid transparent;
  border-bottom-width: 20px;
  border-bottom-style: solid;
}
.dropdown-content:before {
  top: -21px; /* extra -1 pixel offset at the top */
  border-bottom-color: red;
}
.dropdown-content:after {
  top: -20px;
  border-bottom-color: yellow;
}

＆＃13;

＆＃13;

.dropdown {
  position: relative;
  vertical-align: middle;
  display: inline-block;
}

.dropdown-content {
  position: absolute;
  min-width: 160px;
  background-color: yellow;
  padding: 12px 16px;
  margin-top: 20px;
  z-index: 1;
  border-color: red;
  border-width: thin;
  border-style: solid;
}

.dropdown-content a {
  display: block;
}

.dropdown-content:before,
.dropdown-content:after {
  position: absolute;
  left: 70%;
  width: 0;
  height: 0;
  content: '';
  border-left: 20px solid transparent;
  border-right: 20px solid transparent;
  border-bottom-width: 20px;
  border-bottom-style: solid;
}

.dropdown-content:before {
  top: -21px; /* extra -1 pixel offset at the top */
  border-bottom-color: red;
}

.dropdown-content:after {
  top: -20px;
  border-bottom-color: yellow;
}

＆＃13;

<div class='dropdown'>
  <div class="dropdown-content">
    <a href="#">Link 1</a>
    <a href="#">Link 2</a>
    <a href="#">Link 3</a>
  </div>
</div>

＆＃13;

＆＃13;

＆＃13;

Answer 2

尝试创建较小的内部三角形。

检查此答案：Adding border to CSS triangle

而且：CSS triangle custom border color