Why is my navigation bar not covering the whole screen?

Question

The following is the html and css code for the navigation bar.

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


h2,
h3,
a {
	color: #727475;
}

a {
	text-decoration: none;
}



.logo {
	margin: 0;
	font-size: 1.45em;
}

.main-nav {
	margin-top: 5px;

}
.logo a,
.main-nav a {
	padding: 10px 15px;
	text-transform: uppercase;
	text-align: center;
	display: block;
}

.main-nav a {
	color: #456279;
	font-size: .99em;
}

.main-nav a:hover {
	color: #3b556e;
}



.header {
	padding-top: .5em;
	padding-bottom: .5em;
	border: 1px solid #929292;
	background-color: #252323;
	-webkit-box-shadow: 0px 0px 14px 0px rgba(0,0,0,0.75);
	-moz-box-shadow: 0px 0px 14px 0px rgba(0,0,0,0.75);
	box-shadow: 0px 0px 14px 0px rgba(0,0,0,0.75);
	-webkit-border-radius: 5px;
	-moz-border-radius: 5px;
	border-radius: 5px;
}







@media (min-width: 769px) {
	.header,
	.main-nav {
		display: flex;
	}
	.header {
		flex-direction: column;
		align-items: center;
    	/* .header{
		width: 80%;
		margin: 0 auto;
		max-width: 1150px;
	} */
	}

}

@media (min-width: 1025px) {
	.header {
		flex-direction: row;
		justify-content: space-between;
	}

}

<header class="header">
    <h1 class="logo"><a href="#">Dairy Farm Dashboard</a></h1>
      <ul class="main-nav">
          
          <li>
              <select name="" id="" class="form form-control abcdefgh" [(ngModel)]="selecteddate"  (change)="mychange()">
                  <option value="" disabled>Date</option>
                  <option value="{{date}}" *ngFor="let date of date_new">{{date}}</option>
                 
                </select>
          </li>
          <li>
              <select name="" id="" class="form form-control abcdefgh" [(ngModel)]="selectcity"  (change)="citychange()">
                  <option value="" disabled>Country</option>
                  <option value="{{city.country}}" *ngFor="let city of city">{{city.city}}</option>
                  
                 
                </select>
          </li>
          <li><a (click)="logout()">Logout</a></li>
      </ul>
  </header>

The output that I am getting is somewhat like this.

As it is clear from the picture,my navigation bar is not covering the whole screen.However even this would have been acceptable to me . The problem is that when I try to increase the browser size by pressing 'CTRL+' ,the navigation bar is not able to cover up the content below it.The following is the screenshot on expanded screens.

What am I doing wrong here?How do I make the navigation bar cover the entire screen.

Answer 1

I have edited your code.

I have just added margin: 0; to body as by default browsers add some margins to it. It is working fine now.

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

body {
  margin: 0;
}

h2,
h3,
a {
	color: #727475;
}

a {
	text-decoration: none;
}



.logo {
	margin: 0;
	font-size: 1.45em;
}

.main-nav {
	margin-top: 5px;

}
.logo a,
.main-nav a {
	padding: 10px 15px;
	text-transform: uppercase;
	text-align: center;
	display: block;
}

.main-nav a {
	color: #456279;
	font-size: .99em;
}

.main-nav a:hover {
	color: #3b556e;
}



.header {
	padding-top: .5em;
	padding-bottom: .5em;
	border: 1px solid #929292;
	background-color: #252323;
	-webkit-box-shadow: 0px 0px 14px 0px rgba(0,0,0,0.75);
	-moz-box-shadow: 0px 0px 14px 0px rgba(0,0,0,0.75);
	box-shadow: 0px 0px 14px 0px rgba(0,0,0,0.75);
	-webkit-border-radius: 5px;
	-moz-border-radius: 5px;
	border-radius: 5px;
}







@media (min-width: 769px) {
	.header,
	.main-nav {
		display: flex;
	}
	.header {
		flex-direction: column;
		align-items: center;
    	/* .header{
		width: 80%;
		margin: 0 auto;
		max-width: 1150px;
	} */
	}

}

@media (min-width: 1025px) {
	.header {
		flex-direction: row;
		justify-content: space-between;
	}

}

<header class="header">
    <h1 class="logo"><a href="#">Dairy Farm Dashboard</a></h1>
      <ul class="main-nav">
          
          <li>
              <select name="" id="" class="form form-control abcdefgh" [(ngModel)]="selecteddate"  (change)="mychange()">
                  <option value="" disabled>Date</option>
                  <option value="{{date}}" *ngFor="let date of date_new">{{date}}</option>
                 
                </select>
          </li>
          <li>
              <select name="" id="" class="form form-control abcdefgh" [(ngModel)]="selectcity"  (change)="citychange()">
                  <option value="" disabled>Country</option>
                  <option value="{{city.country}}" *ngFor="let city of city">{{city.city}}</option>
                  
                 
                </select>
          </li>
          <li><a (click)="logout()">Logout</a></li>
      </ul>
  </header>

Answer 2

add any one from below in your css because some browser has default margins.

body{
margin:0;
}

or

*{
margin:0;
}