Tryit HTML

<!DOCTYPE html>
<html>
<head>
<style>

body {
  overflow: hidden;
}

header #inner_header_post_thumb {
  background-position: center;
  background-size: cover;
  position: relative;
  background-image: url(files/bg.jpg);
  height: 100%;
}
header #inner_header_post_thumb .dark_overlay {
  position: relative;
  left: 0;
  top: 0;
  right: 0;
  bottom: 0;
  background-color: rgba(0, 0, 0, 0.75);
  height: 500px;
  width: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
}
header #inner_header_post_thumb .dark_overlay .container .header-txt {
  color: #ffffff;
}
header #inner_header_post_thumb .dark_overlay .container .header-txt h1 {
  font-size: 40px;
  color: #ffffff;
  text-transform: uppercase;
}

</style>
</head>
<body>

<header>
 <div id="inner_header_post_thumb">
  <div class="dark_overlay">
   <div class="container">
    <div class="row header-txt text-center">
     <div class="col-xs-12 col-sm-12">
       <h1>Salam Khobi?</h1>
       <h2>Man Sadegh Asadi Hastam</h2>
       <h2>Man Sadegh Asadi Hastam</h2>
       <h2>Man Sadegh Asadi Hastam</h2>
       <h2>Man Sadegh Asadi Hastam</h2>
     </div>  
    </div>
   </div>
  </div>
 </div>
</header>

</body>
</html>

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