cssOMS/nav.scss

body > nav {
    width: 250px;
    overflow-y: auto;
    font-size: 0.8em;
    background: var(--nav-category-background);
    color: rgba(255, 255, 255, 0.8);
}

#nav-side {
    flex: 0;
    display: flex;
    flex-flow: column;
    box-sizing: border-box;
    border-top: 1px solid #4b5055;

    span {
         flex-grow: 1;
    }

    input {
        display: none;

        &:checked + ul {
            .expand {
                transition: all .3s ease;
                display: inherit;
                transform: rotateZ(90deg);
            }

            > li:nth-child(n+2) {
                display: inherit;
            }
        }
    }

    input + ul {
        .expand {
            font-size: .6rem;
            transition: all .3s ease;
            margin-left: 1rem;
            transform: rotateZ(0deg);
        }

        > li:nth-child(n+2) {
            display: none;
        }
    }

    label {
        display: flex;
        align-items: center;
        padding: .5rem 1rem .5rem 1rem;
        cursor: pointer;
    }

    > li {
        display: block;

        a {
            display: block;
            padding: .5rem 1rem .5rem 1rem;
            border-left: 3px solid transparent;

            &:hover, &:focus {
                background: var(--nav-sub-background-hover);
                border-left: 3px solid var(--nav-sub-background-highlight);
            }
        }

        li {
            &:not(:first-child) {
                background: var(--nav-sub-background);
            }

            a {
                &:hover, &.active, &:focus {
                    background: var(--nav-category-background-hover);
                }
            }
        }


        li:first-child {
            border-bottom: 1px solid #212628;
        }

        li:first-child {
            border-top: 1px solid #4b5055;
        }
    }

    > li:first-child {
        li:first-child {
            border-top: none;
        }
    }

    i {
        margin-right: 5px;
        flex-grow: 0;
    }
}

.nav-trigger {
    position: absolute;
    clip: rect(0, 0, 0, 0);

    &:checked + nav {
        width: 0%;
    }
}

.nav-top {
    user-select: none;
    margin-top: 1rem;
    display: block;

    > li {
        > a {
            box-shadow: 0 0 10px 3px rgba(90, 71, 114, 0.1);
            margin-right: .5rem;
            display: inline-block;
            padding: 10px 10px;
        }
    }

    li {
        display: inline-block;
        a {
            background: #fff;
            position: relative;
            cursor: pointer;

            &:hover, &.active, &:focus {
                background: var(--nav-content-hover);
                color: var(--text-on-background-color-2);

                > ul {
                    display: block;
                    opacity: 1;
                    visibility: visible;
                }
            }

            > ul {
                padding: 0;
                z-index: 5;
                position: absolute;
                top: 36px;
                left: 0;
                width: 150px;
                display: none;
                opacity: 0;
                visibility: hidden;

                li {
                    display: block;
                    color: #000;
                    padding: 7px;

                    &:hover, &:focus {
                        color: #252525;
                        background: var(--nav-content-hover);
                    }
                }
            }
        }
    }
}

@media only screen and (max-width: 800px) {
    #nav-trigger:not(:checked) + nav {
        width: 0%;
    }

    #nav-trigger:checked + nav {
        width: auto;
        min-width: 250px;
    }
}

@media only screen and (max-width: 500px) {
    #nav-trigger:checked + nav {
        width: 100%;
    }

    #nav-trigger:checked ~ main {
        display: none;
    }
}