<header class="header">
        <div class="header__container">
            <div class="header-top">
                <div class="header-top__logo">INRES</div>
                <ul class="header-top__nav nav">
                    <li class="nav__item current">
                        <a href="" class="nav__link">Главная</a>
                    </li>
    
                    <li class="nav__item">
                        <a href="" class="nav__link">Новости</a>
                    </li>
    
                    <li class="nav__item">
                        <a href="" class="nav__link">Форум</a>
                    </li>
                    
                    <li class="nav__item">
                        <a href="" class="nav__link">Личный кабинет</a>
                    </li>
                </ul>
            </div>
        </div>
    </header>

* {
  padding: 0;
  margin: 0;
}

body{
  height: 100vh;
}

button {
  cursor: pointer;
  border: 0;
  outline: 0;
}

ul li {
  list-style: none;
}

input{
  border: 0;
  outline: 0;
}


h1, h2, h3, h4, h5, h6 {
  font-size: inherit;
  font-weight: inherit;
}

a{
  text-decoration: none;
}

/*======================================*/

.header {
    background: #fff;
    border-bottom: 1px solid #e2e2e2;
    position: relative;
    z-index: 100;
}
.header__container {
    width: 97%;
    margin: 0 auto;
}

.header-top {
    display: flex;
    align-items: center;
    position: relative;
    background: #fff;
}

.header-top__logo {
    font-size: 1.9em;
    width: 100%;
    flex: 0 0 10%;
    color: #444;
    font-size: 34px;
    font-weight: 700;
}
.header-top__nav {
    display: flex;
    gap: 25px;
    width: 100%;
    flex: 0 0 90%;
}

.nav__item {
    position: relative;
    padding-top: 9px;
    &:hover{
        &::after{
            height: 8px;
        }
    }
    
    &::after{
        content: '';
        position: absolute;
        width: 100%;
        height: 0px;
        top: 0;
        left: 0;
        background: gray;
        transition: all .3s linear;
    }

    &.current{
        &::after{
            background: #000;
            height: 8px;
        }
    }
}

.nav__link {
    line-height: 55px;
    font-size: 14px;
    color: #888;
}