body {
    font-family: Arial, Helvetica, sans-serif;
}
.mobile-container {
    max-width: 48opx;
    margin: auto;
    height: 500px;
    color: white;
    border-radius: 10px;
}
.topnav {
    overflow: hidden;
    background-color: #333;
    position: relative;
}
.topnav #myLink {
    display: none;
}
.topnav a{
    color: white;
    padding: 14px 16px;
    text-decoration: none;
    font-size: 17px;
    display: block;
}
.topnav a.icon {
    background: red;
    display: block;
    position: absolute;
    right: 0;
    top: 0;
}
.topnav a:hover {
    background-color: #ddd;
    color: red;
}
.active {
    background-color: #04AA6d;
    color: red;
}
.footer {
    text-align: center;
    padding: 20px;
    background-color: red; /* You can change the background color */
    color: white; /* Change the text color */
    position: relative;
    bottom: 0;
    width: 100%;
}
body {
    font-family: Arial, Helvetica, sans-serif;
  }
  .mobile-container {
    max-width: 350px;
    margin: auto;
    background-color: red;
    height: 500px;
    color: red;
    border-radius: 10px;
  }
  .topnav {
    overflow: hidden;
    background-color: red;
    position: relative;
  }
  .topnav #myLinks {
    display: none;
  }
  .topnav a {
    color: white;
    padding: 1px 1px;
    text-decoration: none;
    font-size: 17px;
    display: block;
  }
  .topnav a.icon {
    background: #599;
    display: block;
    position: absolute;
    right: 0;
    top: 0;
  }
  .topnav a:hover {
    background-color: #ddd;
    color: red;
  }
  .active {
    background-color: #599;
    color: white;
  }
  .grid-container {
    display: grid;
    grid-template-columns: auto auto auto;
    padding: 10px;
  }
  .grid-item {
    border: 1px;
    padding: 20px;
    font-size: 30px;
    text-align: center;
  }
  ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    background-color: black;
  }
  li {
    float: left;
  }
  li a {
    display: block;
    color: red;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
  }  
  li a:hover {
      display: block;
      color: black;
      text-align: center;
      padding: 14px 16px;
      text-decoration: none;
  }
  li a:hover {
    background-color: red;
  }
#header {
grid-area: header;
}
#content {
grid-area: content;
}
#footer {
grid-area: footer;
}
* {
  box-sizing: border-box;
}

.row::after {
  content: "";
  clear: both;
  display: table;
}

[class*="col-"] {
  float: left;
  padding: 15px;
}

html {
  font-family: "Lucida Sans", sans-serif;
}

.header {
  background-color: #9933cc;
  color: #ffffff;
  padding: 15px;
}

.menu ul {
  list-style-type: none;
  margin: 0;
  padding: 0;
}

.aside {
  background-color: #33b5e5;
  padding: 15px;
  color: #ffffff;
  text-align: center;
  font-size: 14px;
  box-shadow: 0 1px 3px rgba(0,0,0,0.12), 0 1px 2px rgba(0,0,0,0.24);
}

For mobile phones:
[class*="col-"] {
  width: 100%;
}

@media only screen and (min-width: 600px) {
  /* For tablets: */
p {
  font-size: 40px;
}
img {
  opacity: 0.5;
}
}
@media only screen and (min-width: 1200px) {
  /* For desktop: */
  p {
    font-size: 60px;
  }
  img {
    opacity: 0.10;
  }
}
img {
  width: 100vw;
}
.center {
  display: block;
  margin-left: auto;
  margin-right: auto;
  width: 50%;
}