Help, Customise Ivory Search to look like a Car Registration Plate

need help to Customise Ivory Search to look like a Car Registration Plate. Here is the CSS but how to do I go about linking to the Ivory Search CSS:

@font-face {
font-family: ‘uknumberplateregular’;
src: url(‘../fonts/uknumberplate-webfont.woff2’) format(‘woff2’),
url(‘../fonts/uknumberplate-webfont.woff’) format(‘woff’);
font-weight: normal;
font-style: normal;

}

/* Large number plate */
.plate-wrapper {
width: 828px;
max-height:152px;
display: -ms-flex;
display: -webkit-flex;
display: flex;
margin: 32px 0;
background: linear-gradient(to bottom, #f8d038 0%,#f5ca2e 100%);
border-radius: 5px;
line-height: 1;
}
/* The blue section of the plate */
.euGB-plate__container {
width: 12.5%;
}
.euGB-plate__bg {
height: 100%;
max-height: 152px;
background: #063298;
border-radius: 5px 0 0 5px;
text-align: center;
}
/* EU Stars Symbol */
.euGB-plate__eu {
display: block;
width: 75px;
height:75px;
position: relative;
top: 0.5em;
left: 0.5em;
background-image: url(../img/euStarsSmall.png);
background-repeat: no-repeat;
background-position: 0% 0%;
background-size: cover;
font-size: 2em;
}
/* EU Country Code */
.euGB-plate__cc {
display: block;
position: relative;
top: 1.2em;
font-family: ‘uknumberplateregular’, ariel, sans-serif;
font-size: 2em;
font-weight: normal;
color: #f5ca2e;
}
/* The yellow part of the plate */
.registration-ui__container {
width: 87.5%;
}

.registration-ui {
padding: 0em;
font-weight: normal;
font-size: 9em;
border-radius: 6px;
font-family: ‘uknumberplateregular’, ariel, sans-serif;
line-height: 1;
text-align: center;
}