Putting "border", then a border thickness (up to 10px at max right now), then a style, (only solid right now), and then a color, will lead to a border being put on an element.
You can also do this with border color, and put "borderColor" before putting a color.
You can also do either of these but specify a direction after the property (border or borderColor), leading to only that side having that border style.
<span class="border3pxSolidRed colorYellow">Hello World</span><span class="border3pxSolidRed borderColorYellow colorYellow">Hello World</span><span class="border3pxSolidRed borderColorLeftYellow colorYellow">Hello World</span>
Hello WorldHello WorldHello World