Hi there,
The reference site is using custom CSS.
Try adding this:
.navigation-search input[type="search"], .navigation-search input[type="search"]:active, .navigation-search input[type="search"]:focus {
color: #1d2b46;
font-size: 20px;
font-weight: bold;
height: auto !important;
}
@media only screen and (max-width: 600px) {
.navigation-search.nav-search-active {
background-color: rgba(255,255,255,0.95);
margin: 10px 10px 10px 30px;
left: 25%;
height: 37px;
width: 57%;
}
}
@media only screen and (min-width: 600px) {
.navigation-search.nav-search-active {
background-color: white;
margin: 10px 10px 10px 30px;
left: 55%;
height: 37px;
width: 37%;
overflow: hidden;
}
}