style.css

@import url('https://fonts.googleapis.com/css2?family=Dongle:wght@300;400;700&display=swap');

/* Variables */
:root {
    --primary-font-color: rgb(255, 255, 255);
    --secondary-font-color-black: #000000;
    --secondary-font-color-grey: rgb(115, 111, 111);
    --secondary-font-color-gold: goldenrod;
    --body-bg-white: rgb(255, 255, 255);
    --body-bg-black: #000000;
    --body-bg-grey: rgb(115, 111, 111);
}

/* Global config */
html {
    /*
  padding: 0.5rem;
   */
    box-sizing: border-box;
    --font-family: 'Open Sans', sans-serif;
    scroll-behavior: smooth;
    background-color: #ffffff;
}

/* Navigation */
body {
    display: block;
    justify-content: center;
    align-items: center;
    background: var(--body-bg-white);
}

ul {
    display: flex;
    flex-direction: row;
    list-style-type: none;
}

ul li {
    margin: 0.5rem;
}

ul li a {
    position: relative;
    display: block;
    padding: 1rem;
    color: var(--secondary-font-color-black);
    text-decoration: none;
    text-transform: uppercase;
    transition: 0.5s;
}

ul li a::after {
    position: absolute;
    content: "";
    top: 80%;
    left: 0;
    width: 100%;
    height: 3px;
    background: lightslategrey;
    transform: scaleX(0);
    transform-origin: right;
    transition: transform 1s;
}

ul li a:hover::after {
    transform: scaleX(1);
    transform-origin: left;
}