## REM * Good for text. ## EM * Good for padding, margin, and width. * When it isn't applied to the font size property, it becomes relative to the font size of its own element. * Not good for font size because it becomes relative to the font size of the parent element. ## Percentages * They are always relative to their parent. ## VW, VH * Use VW if you don't want the width to be relative to their parent. It is relative to the viewport width instead. * VH is the same as VW, but for height instead of width. ## CH * It measures the width of the character 0 on your font. * It can be used to set a max width on a paragraph. * It works better than rem and em for setting text width because it lets you specifically specify the number of characters per line. * As a rule of thumb, paragraphs should have a length per line of around 54 to 75 characters.