Hi

Thanks for contacting us. Use this custom CSS and set the height which you want and also set the background color which you want.

.logo-image {
    height: 90px !important;
}

#sp-header {
    background: #cccccc !important;
}

Path towards custom CSS: Extensions>Templates>Styles> Click on your current default template name then choose Template Options. Then find custom CSS within the custom code.

-Regards.