select#MECountryListing, select#ukcountry_region {
   
 width: 100%!important;
}
form keygen, select {
    height: unset !important;
    border-radius: none !important;
    color: unset !important;
}
.formdiv {
    margin-top: 50px;
}
.formdiv {
    background: unset;
    border: unset;
}
<style>
/* --- Fix: #MECountryListing width/height in the newsletter form ---
   service-desk-sdp.css declares `select#MECountryListing{border:1px solid #000}`
   at the same specificity (0,1,1,1) as the third-party rule supplying the sizing,
   so load order decides the winner. Scoping to .formsec raises specificity to
   (0,1,2,1) and wins regardless of stylesheet order. */
.formsec .slt-parent {
    position: relative;
    display: block;
    width: 100%;
}
.formsec .form-fields {
    width: 90%;
    max-width: 500px;
    margin: 15px auto;
}
.formsec select#MECountryListing {
    display: block;
    width: 100%;
    box-sizing: border-box;
    padding: 15px 20px;
    font-size: 17px;
    line-height: normal;
    height: auto;
    color: #000;
    border: 0;
    border-radius: 2px;
    outline: 0;
    margin: 0;
    -webkit-appearance: none;
    -moz-appearance: none;
    appearance: none;
    background: #fff url(https://www.manageengine.com/academy/images/dropdown-arrow.png) no-repeat right 9px center;
}
</style>