The Id Selector matches a element based on its id attribute.

em − A relative measurement for the height of a font in em spaces. Because an em unit is equivalent to the size of a given font, if you assign a font to 12pt, each "em" unit would be 12pt; thus, 2em would be 24pt.

The font-weight property is used to increase or decrease how bold or light a font appears.

The border-top-style changes the style of top border.

The background-color property is used to specify the background color of an element. The background of an element covers the total size, including the padding and border and excluding margin.

The color property in CSS is used to set the color of HTML elements. Typically, this property is used to set the font color of an element. In CSS, we use color values for specifying the color. We can also use this property for the border-color and other decorative effects.

The font-size property in CSS is used to specify the height and size of the font. It affects the size of the text of an element. Its default value is medium and can be applied to every element.

If you want to use inline CSS, you should use the style attribute to the relevant tag. The inline CSS is also a method to insert style sheets in HTML document. This method mitigates some advantages of style sheets so it is advised to use this method sparingly.

The negative values are not allowed when using the padding property.

The letter-spacing property in CSS is used to control the space between every letter inside an element or the block of text. It sets the spacing behavior between the characters of the text. Using this property, we can increase or decrease the space between the characters of the text.