How to force .header to span the full width of the page?

/*
  AGENCY - A Treehouse template
  by: http://teamtreehouse.com
  v.1.0.1
  License: MIT http://opensource.org/licenses/MIT
*/

/*Main*/

body{
  color: #B1B9C1;
  font-size: 1em;
  font-weight: 200;
  font-family: 'Roboto', Helvetica, Arial, serif;
  width: 100%;
  text-align: center;
  padding-top: 50px;
}

a {
  color: #5FB6E1;
  text-decoration: none;
}

a:hover {
  color: #53A4C4;
}

img {
  width: 100%;
}

ul li {
  list-style-type: none;
}

.row {
  max-width: 1280px;
  margin: 0 auto;
}

/*Typography*/
p {
  margin-bottom: 40px;
}
h1, h2 {
  font-weight: 400;
  width: 100%;
}
h1 {
  ;
}
h2 {
  font-size: 42px;
  color: #465058;
  margin: 40px 0 0;
}
h3 {
  font-weight: 400;
  font-size: 24px;
  margin: 40px 0 0;
  color: #465058;
}
h4 {
  font-weight: 200;
  font-size: 24px;
  margin: 10px 0 0;
}
h5 {
  font-weight: 300;
  font-size: 20px;
  margin: 10px 0 40px;
}

/*Logo*/
.logo {
  width: 80px;
  height: 24px;
  display: block;
  float: left;
  margin: 20px 0;
  background: url('../img/logo.svg') left center no-repeat;
  background-size: 80px 16px;
}
.description {
  line-height: 60px;
  width: 100%;
  font-size: 1em;
  font-weight: 300;
  margin: 0;
  padding: 0;
  display: block;
}

/*Nav*/
nav {
  float: right;
}
nav a {
  transition: .35s linear;
  padding: 0 10px;
  font-weight: 500;
  line-height: 60px;
  color: #B1B9C1;
  text-align: right;
}
nav a:last-child {
  padding-right: 0;
}
nav a:hover {
  color: #333;
}
nav a.active {
  color: #465058
}

/*Button*/
.button {
  border: 2px solid #D5DDE4;
  border-radius: 4px;
  padding: 12px 20px;
  color: #777B7E;
  transition: .35s;
  font-weight: 400;
}

.button:hover {
  border-color: #7CCEEE;
}

/*Slides*/
.slides {
  width: 100%;
  height: 100%;
  margin: 0 auto 40px;
}
.slide {
  width: 100%;
  height: 100%;
}
.slide h2 {
  margin: 25% 0 20px;
  color: #fff;
}
.slide p {
  width: 60%;
  margin: 0 20% 40px;
  font-size: 26px;
  color: #fff;
}
.slide .button {
  color: #fff;
  border-color: #fff;
  opacity: .6;
}
.slide .button:hover {
  opacity: 1;
}
.slide img {
  width: 50%;
  margin: 100px 50% 100px 10%;
}
.blue {
  background: #3E89BE;
}
.orange {
  background: #F8835A;
}
.green {
  background: #5ECE7F;
}
.yellow {
  background: #FFD365;
}
.slick-dots {
  position: absolute;
  width: 100%;
  bottom: 20px;
  left: 0;
}
.slick-dots li button:before {
  font-size: 16px;
  color: #fff;
}
.slick-dots li.slick-active button:before {
  color: #fff;
}

/*Footer*/
footer {
  margin: 80px 0;
  float: left;
  width: 100%;
}
.social {
  margin: 0;
  padding: 0;
}
.social li a {
  display: inline-block;
  width: 6px;
  height: 6px;
  border-radius: 50%;
  border: 10px solid #ccc;
  opacity: .65;
  transition: .35s linear;
}
.social li a:hover {
  opacity: 1;
}
.social .pink {
  border-color: #FF8DB3
}
.social .light-blue {
  border-color: #7CCEEE
}
.social .dark-blue {
  border-color: #3E89BE
}

/*Work Page*/
.frame {
  padding: 20%;
  border-radius: 10px;
  margin: 40px 10px 0;
}
.item {
  margin-bottom: 40px;
}

/*Sticky*/
.is-sticky h5 {
  width: 100%;
  position: fixed;
  top: 0px;
  background: #fff;
  padding: 12px 0;
  margin: 0;
  opacity: .95;
}

/*Team*/
.team {
  margin-bottom: 60px;
}
.avatar {
  width: 50%;
  display: block;
  border-radius: 50%;
  margin: 0 25%;
}

/*Grid*/
.grid-full {
  width: 100%;
  float: left;
}
.grid-half {
  width: 50%;
  float: left;
}
.grid-third {
  width: 27.33333%;
  margin: 0 3%;
  float: left;
}
.grid-fourth {
  width: 25%;
  float: left;
}
.grid-fifth {
  width: 20%;
  float: left;
}

/*Media Quiries*/
@media (max-width: 1000px) {
  .slides p {
    font-size: 18px;
  }
  .grid-fifth {
    width: 27.333333%;
    margin: 0 3%;
  }
}
@media (max-width: 700px) {
  .logo {
    float: none;
    margin: 20px auto 0;
  }
  .grid-half {
    width: 80%;
    margin: 0 10%;
  }
  .grid-third {
    width: 80%;
    margin: 0 10%;
  }
  .grid-fifth {
    width: 80%;
    margin: 0 10%;
  }
  .row {
    padding: 0 10px;
  }
  nav {
    width: 100%;
  }
  nav a {
    transition: 0s;
    width: 33.333333%;
    float: left;
    padding: 0;
    margin: 10px 0 0;
    text-align: center;
  }
  .description {
    display: none;
  }
  .slide img {
    width: 80%;
    margin: 100px 10%;
  }
  .slick-dots {
    top: 20px;
  }
  .frame {
    margin: 40px 0 0;
  }
  .item {
    margin-bottom: 60px;
  }
  .item h3 {
    margin-top: 20px;
  }
  h4 {
    font-size: 20px;
  }
}



.header {
  background-color: black;
  width: 100%;
}