hehe/user/themes/hehe/scss/template/_header.scss

header{
  position: fixed;
  width: 100%;
  height: 40px;
  top: 0;
  padding: 0 20px;
  display: flex;
  justify-content: space-between;
  background-color: white;
  border-bottom: 2px solid rgb(0,0,0);
  z-index: 999;
  h1{
    margin: auto 0;
  }
  nav{
    margin: auto 0;
    & > .tags{
      & > a {
        li{
          position: relative;
          &::after{
            transition: width 0.5s;
            content: " ";
            position: absolute;
            background: rgb(0, 255, 0);
            width: 0%;
            height: 10px;
            margin: auto;
            z-index: -1;
          }
        }
        li:hover{
          position: relative;
          &::after{
            transition: width 0.5s;
            width: 100%;
          }
        }
      }
    }
    & > ul:nth-child(1) {
      & > li:nth-child(1){
        display: flex;
        position: relative;
        margin-right: 80px;
        &:after{
          content: " ";
          cursor: pointer;
          display: block;
          width: 25px;
          height: 40px;
          background-image: url(../images/fleche2.svg);
          background-repeat: no-repeat;
          background-position: center;
          // background-size: 10px;
          position: absolute;
          right: -25px;
          transition: all 0.5s;
        }
        &.hover{
          &:after{
            transform: rotate(180deg);
            transition: all 0.5s;
          }
        }
      }
    }
  }
  ul{
    display: flex;
    li{
      height: 40px;
      margin-right: 50px;
      align-items: center;
      display: flex;
    }
  }
  ul.tags{
    display: none;
  }
  ul.visible, ul.active{
    display: flex;
    position: absolute;
    top: 40px;
    right: 0px;
    width: auto;
    border-left: 2px solid black;
    border-bottom: 2px solid black;
    z-index: 999;
    background: white;
    a{
      display: flex;
      width: auto;
      height: 50px;
      margin: 0 20px;
      li{
        margin: auto;
      }
    }
  }
}