CSS

Selectors

<div id="test">
<div class="important">
<span>

Properties

      left, right, top, bottom
      width, height
      color, background-color
      border, border-color, border-right-color, etc.
      And many others.

Finding things by selector

      var divsOrSpans = document.querySelectorAll("div, span");
    
      var firstImportantDivOrImage = document.querySelector("div.important, img");