Disclaimer: this tip centers around the use of Alfred but, doesn't require the premium "Power Pack". MDN is...or should be a go-to for anyone doing any level of front-end development. It is an indispensible knowledge base on anything concerning HTML, CSS, or Js. Since Alfred has a great way to add custom searches, we can pipe items into Alfred and have it pass the search onto MDN.
MDN also encodes spaces as + symbols so one will have to check the appropriate box within the Alfred Custom Search settings.
Now, if you have a question about how line-height works you can simply type mdn line-height and BOOM, stupendous success.