header {
    display: flex;
    align-items: center;
    padding: 20px 30px;
    gap: 10px;
    position: relative;
}

header h2 {
    margin: 0;
}

header .site-links,
header .site-links>a:hover {
    color: var(--color-primary);
}

header .site-links>a::after {
    content: '';
    display: block;
    position: absolute;
    left: 0;
    bottom: -4px;
    width: 0;
    height: 2px;
    background-color: currentColor;
    transition: width 0.4s ease-out;
}

header .site-links>a:hover::after {
    width: 100%;
}

header .btn-rect {
    border-radius: 5px;
    padding: 7px 15px;
    background-color: var(--color-primary);
}

header .btn-rect,
header .btn-rect:hover {
    color: var(--color-on-primary);
}

#menu {
    position: fixed;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    background-color: var(--color-primary);
    color: var(--color-on-primary);
    padding: 15px 20px;
    text-align: center;
    gap: 20px;
    opacity: 0;
    pointer-events: none;
    z-index: 1;
}

#menu_btn {
    display: none;
    width: 2em;
    height: 2em;
    align-items: center;
    justify-content: center;
    appearance: none;
    font-family: "Font Awesome 5 Free";
    font-weight: bold;
    font-size: 1.5em;
    cursor: pointer;
    color: var(--color-primary);
    z-index: 2;
}

#menu_btn::before {
    content: '\f0c9';
}

#menu_btn:checked::before {
    content: '\f00d';
    color: var(--color-on-primary);
}

@media screen and (max-width:600px) {
    header .site-links>a,
    header .btn-rect {
        display: none;
    }
    #menu a {
        display: inline-block;
        font-size: 25px;
        font-weight: 500;
    }
    #menu_btn {
        display: flex;
    }
    #menu_btn:checked~#menu {
        opacity: 1;
        pointer-events: all;
    }
}