demo

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <style>
@import url('https://fonts.googleapis.com/css2?family=Poppins:wght@200;300;400;500;600;700&display=swap');
*{
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: 'Poppins', sans-serif;
}
body{
  overflow: hidden;
  background: #f2f2f2;
}
.wrapper{
  position: absolute;
  top: 20px;
  left: 20px;
  animation: show_toast 1s ease forwards;
}
@keyframes show_toast {
  0%{
    transform: translateX(-100%);
  }
  40%{
    transform: translateX(10%);
  }
  80%, 100%{
    transform: translateX(20px);
  }
}
.wrapper.hide{
  animation: hide_toast 1s ease forwards;
}
@keyframes hide_toast {
  0%{
    transform: translateX(20px);
  }
  40%{
    transform: translateX(10%);
  }
  80%, 100%{
    opacity: 0;
    pointer-events: none;
    transform: translateX(-100%);
  }
}
.wrapper .toast{
  background: #fff;
  padding: 20px 15px 20px 20px;
  border-radius: 10px;
  border-left: 5px solid #2ecc71;
  box-shadow: 1px 7px 14px -5px rgba(0,0,0,0.15);
  width: 430px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.wrapper .toast.offline{
  border-color: #ccc;
}
.toast .content{
  display: flex;
  align-items: center;
}
.content .icon{
  font-size: 25px;
  color: #fff;
  height: 50px;
  width: 50px;
  text-align: center;
  line-height: 50px;
  border-radius: 50%;
  background: #2ecc71;
}
.toast.offline .content .icon{
  background: #ccc;
}
.content .details{
  margin-left: 15px;
}
.details span{
  font-size: 20px;
  font-weight: 500;
}
.details p{
  color: #878787;
}
.toast .close-icon{
  color: #878787;
  font-size: 23px;
  cursor: pointer;
  height: 40px;
  width: 40px;
  text-align: center;
  line-height: 40px;
  border-radius: 50%;
  background: #f2f2f2;
  transition: all 0.3s ease;
}
.close-icon:hover{
  background: #efefef;
}
    </style>
  <link rel="stylesheet" href="https://unicons.iconscout.com/release/v3.0.6/css/line.css">
</head>
<body>
  <div class="wrapper">
    <div class="toast">
      <div class="content">
        <div class="icon"><i class="uil uil-wifi"></i></div>
        <div class="details">
        <h2>By Sufian Amjad</h2>
        <h3>Wellcome Here</h3>
          <span>You're online now</span>
          <p>Internet is connected.</p>
          <h4>Run You Code here</h4>
        </div>
      </div>
      <div class="close-icon"><i class="uil uil-times"></i></div>
    </div>
  </div>

function offline(){ //function for offline
        wrapper.classList.remove("hide");
        toast.classList.add("offline");
        title.innerText = "You're offline now";
        subTitle.innerText = "Opps! Internet is disconnected.";
        wifiIcon.innerHTML = '<i class="uil uil-wifi-slash"></i>';
    }

setInterval(()=>{ //this setInterval function call ajax frequently after 100ms
        ajax();
    }, 100);
} 
  
  </script>

</body>
</html>

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