Searc button

body {
font-family: Arial;
}

* {
box-sizing: border-box;
}

form.example input[type=text] {
padding: 10px;
font-size: 17px;
border: 1px solid grey;
float: left;
width: 80%;
background: #f1f1f1;
}

form.example button {
float: left;
width: 20%;
padding: 10px;
background: #2196F3;
color: white;
font-size: 17px;
border: 1px solid grey;
border-left: none;
cursor: pointer;
}

form.example button:hover {
background: #0b7dda;
}

form.example::after {
content: “”;
clear: both;
display: table;
}

Search Button

Full width:

Centered inside a form with max-width: