style.css

body, ul, li, h1, h2, a{
  margin: 0;
  padding: 0;
  font-family: tahoma;
}
p{
  font-size: 18px;
}
header{
  background-color: #F63232;
  padding: 20px 0;
  text-align: center;
  position: fixed;
  width: 100%;
  top: 0;
  left: 0;
  z-index: 1;
}
header h1{
  color: white;
  border: 8px solid white;
  display: inline-block;
  padding: 6px 12px;
  border-radius: 36px;
}
.banner{
  position: relative;
}
.banner img{
  max-width: 100%;
}
.banner .welcome{
  background:#FEB614;
  color: white;
  padding: 30px;
  font-size: 50px;
  position: absolute;
  left: 0;
  top: 40%;
} 
.banner .welcome span{
  font-size: 1.3em;
}
nav{
  background: #F4F4F4;
  padding: 20px;
  position: sticky;
  top: 106px;
  z-index: 1;
}
nav ul{
  white-space: nowrap;
  max-width: 1200px;
  margin: 0 auto;
  text-align: center;
}
nav li{
  width: 25%;
  display: inline-block;
  font-size: 24px;
}
nav li a{
  text-decoration: none;
  color: #4B4B4B;
}
nav li a:hover{
  text-decoration: underline;
}
nav li a.join{
  color: #F63232;
}
main{
  max-width: 100%;
  width: 1200px;
  margin: 80px auto;
  padding: 0 40px;
  box-sizing: border-box;
}
article h2{
  color: #F63232;
  font-size: 48px;
}
article p{
  line-height: 2em;
  color: #4B4B4B;
}
article p::first-line{
  font-weight: bold;
  font-size: 1.2em;
}
.images{
  text-align: center;
  margin: 80px 0;
  white-space: nowrap;
}
.images li{
  display: inline-block;
  list-style-type: none;
  width: 40%;
  margin: 20px 5%;
  position: relative;
}
.images li:hover{
  position: relative;
  top: -4px;
}
.images li img{
  max-width: 100%;
}
section.join{
  background: #F4F4F4;
  text-align: center;
  padding: 60px 20px;
  color: #4B4B4B;
}
section.join h2{
  font-size: 36px;
}
form input{
  margin: 20px 0;
  padding: 10px 20px;
  font-size: 24px;
  border-radius: 28px;
  border: 4px solid white;
}
form input:focus{
  border: 4px dashed #4B4B4B;
  outline: none;
}
form input:valid{
  border: 4px solid #71d300;
}
footer{
  background: #F63232;
  color: white;
  padding: 10px;
  text-align: center;
}

/* Responsive Styles */

@media screen and (max-width: 1400px){

  .banner .welcome h2{
    font-size: 60px;
  } 

  nav li {
    font-size: 18px;
  }
}

@media screen and (max-width: 960px){

  .banner .welcome h2{
    font-size: 40px;
  } 
}

@media screen and (max-width: 700px){

  .banner .welcome {
    position: relative;
    text-align: center;
    padding: 10px;
  } 

  .banner .welcome br{
    display: none;
  } 

  .banner .welcome h2{
    font-size: 25px;
  } 
  .banner .welcome span {
    font-size: 1em;
  }
  .images li {
    width: 100%;
    margin: 20px auto;
    display: block;
  }
}

@media screen and (max-width: 560px) {

  nav li {
    font-size: 20px;
    display: block;
    width: 100%;
    margin: 12px 0;
  }
  header {
    position: relative;
  }
  nav {
    top: 0;
  }
}