 display: flex;
 justify-content: center;
 align-items: center;
 height: 100vh;
 flex-direction: column;

}

.search-box {

 display: flex;
 align-items: center;
 justify-content: center;
 margin-bottom: 20px;

}

.search-box input[type="text"] {

 font-size: 24px;
 padding: 10px;
 width: 400px;
 max-width: 100%;

}

.search-box input[type="submit"] {

 font-size: 24px;
 padding: 10px;

} </style>

Welcome to My Wiki

   <form action="https://wikijoo.ir/index.php" method="get">
     <input type="text" name="search" placeholder="Search..." required>
     <input type="submit" value="Search">
   </form>