<div class="kutu">
  <h1>Tarayıcının genişliğini değiştirin.</h1>
  <ul>
    <li>Küçük</li>
    <li>Orta</li>
    <li>Büyük</li>
  </ul>
</div>

.kutu {
  width: 100%;
  height: 80px;
}

@media (width >= 1100px) {
  body {
    background: #fffa84;
  }
  
  ul li:nth-child(3) {
    background-color: rgba(0, 0, 0, 0.7);
    color: rgb(255,255,255);
  }
}
@media (480px <= width <= 1100px) {
  body {
    background: #50f7b2;
  }
  
  ul li:nth-child(2) {
    background-color: rgba(0, 0, 0, 0.7);
    color: rgb(255,255,255);
  }
}
@media  (width <= 480px) {
  body {
    background: #f95e8a;
  }
  
  ul li:nth-child(1) {
    background-color: rgba(0, 0, 0, 0.7);
    color: rgb(255,255,255);
  }
}

















@import url('https://fonts.googleapis.com/css?family=Merriweather+Sans:300,800');

body {
  font-family: 'Merriweather Sans', sans-serif;
  width: 550px;
  margin-inline: auto;
}

h1 {
  margin-top: 50px;
  text-align: center;
  margin-bottom: 0;
}

h1:after {
  display: block;
  content: " ";
  font-family: "Open Sans", sans-serif;
  font-size: 1rem;
  font-weight: 400;
  letter-spacing: 0.056rem;
  color: rgba(0, 0, 0, 0.5);
  width: 80%;
  margin: 10px auto;
  padding: 0;
  border-top: 2px solid rgba(0, 0, 0, 0.1);
}

ul {
  display: flex;
  flex-direction: row;
  list-style: none;
  justify-content: center;
  margin: 0;
  padding: 0;
}

ul li {
  margin-right: 10px;
  font-size: 18px;
  padding: 5px 10px;
  border-radius: 5px;
}