Some students mistakes and good parts from Kottans frontend cource 2019

button.scss

// Giant unsorted class
/*
* Some sprcific rules better put in global scope
* Use comments to describe sections of class. Example: box-model, typgraphy ...
*/
 &__button-input {
    appearance: none;
    box-sizing: content-box;
    font-family: "ddg-serp-icons";
    speak: none;
    font-style: normal;
    font-weight: normal;
    font-variant: normal;
    text-transform: none;
    text-decoration: none;
    font-smoothing: antialiased;
    osx-font-smoothing: grayscale;
    tap-highlight-color: transparent;
    width: 1em;
    display: block;
    cursor: pointer;
    background: transparent;
    text-align: center;
    border: none;
    position: absolute;
    top: 0;
    bottom: 0;
    right: 2px;
    left: auto;
    margin: auto;
    z-index: 2;
    outline: none;
    border-radius: 0 2px 2px 0;
    min-width: 26px;
    color: #999;
    font-size: 1.25em;
    padding: 0 0.64em;
    height: auto;
    min-height: 1.8em;
    margin-top: -1px;
    margin-bottom: -1px;
    margin-right: -3px;
    line-height: 1.5;
    background-color: transparent;
    background-position: 50% 50%;
    background-repeat: no-repeat;
    font-smoothing: subpixel-antialiased;
}

mixins.scss

//Mixin for media rules
=r($width)
  @media only screen and (max-width: $width+ "px")
    @content

.nav
    font-family: $bebas
    font-size: 16px

    +r(1000)
        position: absolute
        top: -500px

.nav__list
    margin: 0
    padding: 0

    +r(1000)
        flex-direction: column
        justify-content: flex-start

.nav__list::after
    content: ''
    display: none

    +r(1000)
        display: block

.nav__item
    margin-left: 30px
    color: $nav

    +r(1000)
        margin-bottom: 30px

nav.scss

// Hard reading class
.nav{
  display: flex;
  margin: 20px 20px 0 0;
  & li{
    margin-left: 20px;
  }
  &__bell{
    color: $font-color;
    display: block;
    margin-top: 2px;
    @include transition;
    &:hover{
      opacity: 0.8;
    }
  }
  &__auth{
    background-color: #00897b;
    @include transition;
    &::before {
      content: url(../assets/img/photo.png);
    }
    &:hover {
      opacity: .8;
    }
  }
  &__link{
    color: $font-color;
    @include transition;
    &:hover{
      color: $font-color;
      text-decoration: underline;
    }
  }
  &__menu{
    display: none;
    right: 1%;
    &_rect{
      content: "";
      width: 0;
    }
    &_lists{
      display: flex;
      justify-content: space-between;
    }
    &_listsMore{
      display: none;
    }
    & li{
      margin: 1px;
      border-radius: 2px;
      & a{
        color: rgba(0,0,0,0.87);
        @include transition;
        &:focus{
        outline: 3px solid $focused;
        transition: none;
        }
        &:active{
          outline: 2px solid lightgreen;
        }
      }
      &:hover{
        & a{
          border: 1px solid rgba(0,0,0,.2);
        }
        & .nav__menu_title {
          z-index: 3;
          background: rgba(255,255,255,.9);
        }
      }
    }
    &_icon{
      background-image: url(../assets/img/sprite.png);
      background-size: 64px 2410px;
      &-user{
        background-position-y: -70px;
      }
      &-search{
        background-position-y: -1311px;
      }
      &-map{
        background-position-y: -207px;
      }
      &-youtube{
        background-position-y: -550px;
      }
      &-news{
        background-position-y: -1034px;
      }
      &-gmail{
        background-position-y: -1103px;
      }
      &-contacts{
        background-position-y: -2140px;
      }
      &-disk{
        background-position-y: -2002px;
      }
      &-calendar{
        background-position-y: -829px;
      }
      &-google{
        background-position-y: -412px;
      }
      &-translate{
        background-position-y: -1657px;
      }
      &-photo{
        background-position-y: -1519px;
      }
      &-doc{
        background-position-y: 959px;
      }
      &-blogger{
        background-position-y: 339px;
      }
      &-hangout{
        background-position-y: 821px;
      }
      &-keep{
        background-position-y: 1028px;
      }
      &-jamboard{
        background-position-y: 1509px;
      }
      &-class{
        background-position-y: 1789px;
      }
      &-earth{
        background-position-y: 544px;
      }
      &-collection{
        background-position-y: 684px;
      }
    }
    &_title{
      text-align: center;
      display: block;
      text-overflow: ellipsis;
    }
    &_input{
      display: none;
      & ~ label{
        text-align: center;
        background-color: $bg-color;
      }
      &:checked{
        & ~ label{
          height: 2px;
          span{
            display: none;
          }
        }
        & ~ .nav__menu_listsMore{
          display: flex;
          justify-content: flex-start;
        }
        & ~ .nav__menu_linkMore{
          display: block;
          text-align: center;
        }
      }
    }
    &_linkMore{
      display: none;
      font-size: 0.9em;
      &:hover{
        text-decoration: underline;
        opacity: 0.8;
      }
    }
    &_listMore {
      animation-name: google;
      animation-duration: 0.5s;
      animation-timing-function: ease;
      animation-delay: 0s;
      animation-iteration-count: 1;
      animation-direction: normal;
      animation-fill-mode: none;
      animation-play-state: running;
    }
  }
  &__input{
    display: none;
    &_icons{
      top: -1px;
      padding: 0;
      &:hover .nav__input_icon{
        color: #000;
      }
    }
    &_icon{
      display: block;
      font-size: 0.55em;
      @include transition;
      &:after,
      &:before{
        position: absolute;
        content: "■";
        right: calc(100% + 1px);
      }
      &:after{
        left: calc(100% + 1px);
      }
    }
    & ~ label {
      color: #999999;
    }
    &_close{
      animation-fill-mode: none;
      animation-play-state: running;
    }
    &:checked{
      & ~ label{
        color: #000;
        & > .nav__input_close{
          display: block;
        }
        &::before,
        &::after {
          content: '';
          position: absolute;
        }
        &::after {
          border-bottom: 10px solid white;
          top: 32px;
        }
      }
      & ~ .nav__menu{
        display: block;
      }
    }
  }
}

style.css

// Too specific selector
*, body {
  margin: 0;
  padding: 0;
  line-height: 1;
  box-sizing: border-box;
  font-family: arial, sans-serif; }

.header {
  padding: 20px; }

li {
  list-style: none; }

a {
  text-decoration: none;
  color: rgba(0, 0, 0, 0.87);
  line-height: 24px;
  font-size: 14px; }

.navigation {
  display: flex;
  align-items: center; }
  .navigation-list {
    display: -webkit-box;
    display: -webkit-flex;
    position: relative; }
    .navigation-list .list-item {
      margin: 0 10px; }
      .navigation-list .list-item .post:hover,
      .navigation-list .list-item .images:hover {
        border-bottom: 1px solid #000; }
      .navigation-list .list-item:focus {
        outline: none; }
      .navigation-list .list-item .apps-input {
        display: none; }
      .navigation-list .list-item .apps-label .apps-icon {
        width: 20px;
        height: 20px;
        background-size: contain;
        display: block; }
        .navigation-list .list-item .apps-label .apps-icon:hover {
          opacity: 1; }
      .navigation-list .list-item .apps-label .apps-close {
        height: 100vh;
        z-index: -1; }
      .navigation-list .list-item .apps-popup {
        display: none; }
        .navigation-list .list-item .apps-popup:before {
          content: "";
          width: 12px;
          transform: rotate(-45deg); }
        .navigation-list .list-item .apps-popup .wrapper {
          -webkit-box-shadow: 0 2px 10px rgba(0, 0, 0, 0.2);
                  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.2); }
          .navigation-list .list-item .apps-popup .wrapper .apps-popup-block {
            display: flex;
            padding: 15px 20px; }
            .navigation-list .list-item .apps-popup .wrapper .apps-popup-block .popup-item {
              width: 33%;
              text-align: center;
              padding: 6px;
              border: 1px solid #fff; }
              .navigation-list .list-item .apps-popup .wrapper .apps-popup-block .popup-item:hover {
                border: 1px solid #ddd; }
              .navigation-list .list-item .apps-popup .wrapper .apps-popup-block .popup-item .app-image {
                width: 70%;
                height: 50px; }
            .navigation-list .list-item .apps-popup .wrapper .apps-popup-block .other-products {
              width: 100%;
              color: rgba(0, 0, 0, 0.87);
              text-align: center;
              margin-top: 30px; }
              .navigation-list .list-item .apps-popup .wrapper .apps-popup-block .other-products:hover {
                color: #808080; }
            .navigation-list .list-item .apps-popup .wrapper .apps-popup-block .account-image {
                      border-radius: 50%; }
          .navigation-list .list-item .apps-popup .wrapper .additional-items {
            display: none; }
        .navigation-list .list-item .apps-popup .more-apps {
          display: none; }
          .navigation-list .list-item .apps-popup .more-apps:checked ~ .additional-items {
            display: flex; }
          .navigation-list .list-item .apps-popup .more-apps:checked ~ .more-button {
            display: block;
            margin: 0 auto; }
        .navigation-list .list-item .apps-popup .more-button {
          font-size: 14px;
          opacity: 1;
          border: 1px solid #f5f5f5; }
          .navigation-list .list-item .apps-popup .more-button:hover {
            border: 1px solid #ccc; }
    .navigation-list .notify {
      padding: 5px;
      background: #000;
      opacity: 0.5;
      -webkit-border-radius: 20px;
              border-radius: 20px; }
      .navigation-list .notify:hover {
        opacity: 1; }
      .navigation-list .notify-link {
        display: block;
        background-size: 70%; }
    .navigation-list .user {
      -webkit-border-radius: 20px;
              border-radius: 20px;
      position: relative;
      padding: 5px; }
      .navigation-list .user-link {
        background-image: url(https://lh3.googleusercontent.com/-wR45nNlb0jY/AAAAAAAAAAI/AAAAAAAAAAA/ACevoQOrtxfoKv7go3rZDlVl-xoTZ7AifA/s64-c-mo/photo.jpg);
        display: block;
        border-radius: 20px; }

.apps-input:checked ~ .apps-popup {
  display: block;
}

.apps-input:focus ~ .apps-label .apps-icon {
  outline: 2px solid #4d90fe; }

.apps-input:checked + .apps-label > .apps-close {
  display: block; }