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'), a package Title, or certain other fields by prefixing search terms with the field name.
Currently the searchable fields are 'Title', 'Id', 'Description', 'Tags', and 'Author'.
[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. Note that Titles often contain spaces but Package IDs are not allowed to contain spaces, and often contain dots.)]
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.
You can also search for multiple keywords in a single field, here we wish to search only the package description for two keywords 'Metro' and 'modern':
description:Metro description:modern
And you can perform phrase searches
Title:MVC
tags:MVC4
description:validation
description:"javascript library"