To the themes , or template, or sections, custom css
Read: https://help.shopify.com/en/manual/online-store/themes/theme-structure/extend/add-css
Try the following CSS bandaids
Options color (keep in mind changing a background means changing text to high contrast color, and form inputs have limited styling as they are mainly controlled by the operating system)
[name="sort_by"] option {
color: white;
background-color: black;
}
Removing which ones you want to keep from this rule (do not leave a trailing comma):
[value="manual"],
[value="best-selling"],
[value="title-ascending"],
[value="title-descending"],
[value="price-ascending"],
[value="price-descending"],
[value="created-ascending"],
[value="created-descending"] {
display: none;
}
i.e.
[value="manual"],
[value="title-ascending"],
[value="title-descending"],
[value="created-ascending"],
[value="created-descending"] {
display: none;
}
Swapping option positions is more advanced and required modifying theme code directly to build an entirely custom dropdown.
For dawn based themes that’s in several places in the facets.liquid snippet
https://github.com/Shopify/dawn/blob/main/snippets/facets.liquid#L479