Overleaf/services/web/frontend/stylesheets/app/editor/left-menu.less

#left-menu {
  position: absolute;
  width: @left-menu-width;
  padding: (@line-height-computed / 2);
  top: 0;
  bottom: 0;
  background-color: #f4f4f4;
  z-index: 100;
  overflow-y: auto;
  overflow-x: hidden;
  -webkit-transition: left ease-in-out @left-menu-animation-duration;
  transition: left ease-in-out @left-menu-animation-duration;
  font-size: 14px;

  left: -280px;
  &.shown {
    left: 0;
  }

  h4 {
    font-family: @font-family-sans-serif;
    font-weight: 400;
    font-size: 1rem;
    margin: (@line-height-computed / 2) 0;
    padding-bottom: (@line-height-computed / 4);
    color: @gray-light;
    border-bottom: 1px solid @gray-lighter;
  }

  > h4:first-child {
    margin-top: 0;
  }

  ul.nav {
    a {
      cursor: pointer;
      &:hover,
      &:active,
      &:focus {
        background-color: @link-color;
        color: white;
        i {
          color: white;
        }
      }
      i {
        color: @gray;
      }
      padding: (@line-height-computed / 4);
      font-weight: 700;
    }
    .link-disabled {
      color: @gray-light;
    }
  }

  > ul.nav:last-child {
    margin-bottom: @line-height-computed / 2;
  }

  ul.nav-downloads {
    li {
      display: inline-block;
      text-align: center;
      width: 100px;
      a {
        color: @gray-dark;
      }
      i {
        margin: (@line-height-computed / 4) 0;
      }
    }
  }

  form.settings {
    label {
      font-weight: normal;
      color: @gray-dark;
      flex: 1 0 50%;
      margin-bottom: 0;
      margin-top: 9px;
      padding-right: 5px;
      white-space: nowrap;
    }
    button,
    select {
      width: 50%;
      margin: 9px 0;
    }
    .form-controls {
      clear: both;
      padding: 0 9px;
      display: flex;
      flex-wrap: wrap;
      align-items: baseline;
      justify-content: flex-end;
      border-bottom: solid 1px rgba(0, 0, 0, 0.07);
      &:first-child {
        margin-top: -9px;
      }
      &:last-child {
        border-bottom: 0;
      }
      &:hover {
        background-color: @link-color;
        // select.form-control {
        // 	color: white;
        // }
        label,
        i.fa {
          color: white;
        }
      }
      &:after {
        content: '';
        display: table;
        clear: both;
      }
    }
  }
}

#left-menu-mask {
  .full-size;
  opacity: 0.4;
  background-color: #999;
  z-index: 99;
}