.App {
  border: #e0e0e0 1px solid;
  margin: 24px;
}
* {
  box-sizing: border-box;
  font-family: Open Sans, Arial, sans-serif;
}
html,
body {
  margin: 0;
  color: rgba(0, 0, 0, 0.87);
  background-color: #f9f9f9;
}
.nav {
  background-color: #f4f5f6;
  height: 52px;
  line-height: 50px;
  display: flex;
  border: #e0e0e0 1px solid;
}
.nav .select-wrapper {
  position: relative;
  width: 200px;
}
.nav .select-wrapper::before {
  color: #0c81f5;
  font-size: 20px;
  pointer-events: none;
  position: absolute;
  right: 15px;
  top: 10px;
}
.nav select {
  background: #f4f5f6;
  border: none;
  border: 1px #0c81f5 solid;
  color: #0c81f5;
  cursor: pointer;
  font-family: 'Open Sans', sans-serif;
  font-size: 16px;
  height: 40px;
  outline: none;
  padding-left: 10px;
  width: 100%;
}
.nav select option {
  color: #0c81f5;
}
.nav select::-ms-expand {
  display: none;
}
.nav select:focus::-ms-value {
  background-color: transparent;
}
.nav input[type=number] {
  height: 40px;
  border: 1px solid #0c81f5;
  background: none;
  color: #0c81f5;
  padding: 0px 5px;
}
.nav button {
  height: 40px;
  border: 1px solid #0c81f5;
  background: #0c81f5;
  color: #FFF;
}
.studentList {
  display: flex;
  flex-wrap: wrap;
}
.studentList .user {
  border: 1px solid #454545;
  margin: 5px;
  padding: 5px;
  transition: cubic-bezier(0.075, 0.82, 0.165, 1) 1000ms;
}
.studentList .user.disappear {
  opacity: 0.09;
  transition: cubic-bezier(0.075, 0.82, 0.165, 1) 1000ms;
}
.studentList .user.appear {
  opacity: 1;
  transition: cubic-bezier(0.075, 0.82, 0.165, 1) 1000ms;
}
.studentList .user .user_img img {
  width: 200px;
}
.studentList .user .username {
  text-align: center;
  display: inline-block;
  width: 200px;
}