Common HTML and CSS miscues as explained by WTF, HTML and CSS?.

• Declare a doctype
• Box model math
• Rem units and Mobile Safari
• Floats first
• Floats and clearing
• Floats and computed height
• Floated are block level
• Vertical margins often collapse
• Styling table rows
• Firefox and <input> buttons
• Firefox inner outline on buttons
• Always set a type on <button>s
• Internet Explorer’s selector limit
• Position explained
• Position and width
• Fixed position and transforms

Thanks to, CSS Weekly #103 and WTF, HTML and CSS?.