NuGet package search works the same whether you use the nuget.org website, or the Visual Studio Extensions.
modern UI javascript
Search will do its best effort to find relevant documents containing all 3 keywords, and return matching documents.
"modern UI" package
Entering a phrase between quotation marks ("") change the search to look for the particular phrase instead of separate keywords. Matching documents should usually contain the exact phrase "modern UI", including variations on capitalization e.g. "Modern ui", and also usually contain the word 'package'.
You can search for a specific package ID (or 'Id' or 'id'), or certain other fields by prefixing search terms with the field name.
Currently the searchable fields are 'Id', 'Version', 'Tags', 'Author', and 'Owner'.
[What's the difference between ID and Title? ID is the name you use in package management console. Title is what is shown at the top of the package page in search results.]
ID:jQuery
id:NuGet.Core
finds packages with "jQuery" or "NuGet.Core" in their ID field respectively.
Id:"Nuget.Core"
is another way to find packages with "NuGet.Core" in their ID field.
The 'Id' filter is a substring match, so if you search for the following:
Id:jquery
You'll get results like 'jQuery.UI.Combined' and 'jQuery.Validation'. If you want to perform an exact search, use the 'packageid' field. This will filter to show only the one package with the ID you specified (or nothing if there is no package with that ID). For example:
PackageId:jquery
You can also search for multiple keywords in a single field. Or mix and match fields.
id:jquery tags:validation
id:jquery id:ui
And you can perform phrase searches:
id:"jquery.ui"
Finally, if you use a field we don't support, such as 'title', we'll just ignore it and search all the fields. So the following query
title:jquery ui
Is interpreted exactly the same as this query:
jquery ui