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border-top

The border-top CSS property is a shorthand that sets the values of border-top-color, border-top-style, and border-top-width. These properties describe the top border of elements.

The three values of the shorthand property can be specified in any order, and one or two of them may be omitted.

As with all shorthand properties, border-top always sets the values of all of the properties that it can set, even if they are not specified. It sets those that are not specified to their default values. This means that:

border-top-style: dotted;
border-top: thick green;

is actually the same as

border-top-style: dotted;
border-top: none thick green;

and the value of border-top-style given before border-top is ignored.

Since the default value of border-top-style is none, not specifying the border-style part of the value means that the property specifies its default value which is none and means no border.

Initial value	as each of the properties of the shorthand: `border-top-width`: `medium` `border-top-style`: `none` `border-top-color`: `currentcolor`
Applies to	all elements. It also applies to `::first-letter`.
Inherited	no
Media	visual
Computed value	as each of the properties of the shorthand: `border-top-width`: the absolute length or `0` if `border-top-style` is `none` or `hidden` `border-top-style`: as specified `border-top-color`: If the value is translucent, the computed value will be the `rgba()` corresponding one. If it isn't, it will be the `rgb()` corresponding one. The `transparent` keyword maps to `rgba(0,0,0,0)`.
Animation type	as each of the properties of the shorthand: `border-top-color`: a color `border-top-style`: discrete `border-top-width`: a length
Canonical order	order of appearance in the formal grammar of the values

Syntax

border-top: 1px;
border-top: 2px dotted;
border-top: medium dashed green;

Values

<br-width>: See border-top-width.
<br-style>: See border-top-style.
<color>: See border-top-color.

Formal syntax

<br-width> || <br-style> || <color>where 
<br-width> = <length> | thin | medium | thick
<br-style> = none | hidden | dotted | dashed | solid | double | groove | ridge | inset | outset
<color> = <rgb()> | <rgba()> | <hsl()> | <hsla()> | <hex-color> | <named-color> | currentcolor | <deprecated-system-color>
where 
<rgb()> = rgb( <rgb-component>#{3} )
<rgba()> = rgba( <rgb-component>#{3} , <alpha-value> )
<hsl()> = hsl( <hue>, <percentage>, <percentage> )
<hsla()> = hsla( <hue>, <percentage>, <percentage>, <alpha-value> )
<named-color> = transparent | aliceblue | antiquewhite | aqua | aquamarine | azure | beige | bisque | black | blanchedalmond | blue | blueviolet | brown | burlywood | cadetblue | chartreuse | chocolate | coral | cornflowerblue | cornsilk | crimson | cyan | darkblue | darkcyan | darkgoldenrod | darkgray | darkgreen | darkgrey | darkkhaki | darkmagenta | darkolivegreen | darkorange | darkorchid | darkred | darksalmon | darkseagreen | darkslateblue | darkslategray | darkslategrey | darkturquoise | darkviolet | deeppink | deepskyblue | dimgray | dimgrey | dodgerblue | firebrick | floralwhite | forestgreen | fuchsia | gainsboro | ghostwhite | gold | goldenrod | gray | green | greenyellow | grey | honeydew | hotpink | indianred | indigo | ivory | khaki | lavender | lavenderblush | lawngreen | lemonchiffon | lightblue | lightcoral | lightcyan | lightgoldenrodyellow | lightgray | lightgreen | lightgrey | lightpink | lightsalmon | lightseagreen | lightskyblue | lightslategray | lightslategrey | lightsteelblue | lightyellow | lime | limegreen | linen | magenta | maroon | mediumaquamarine | mediumblue | mediumorchid | mediumpurple | mediumseagreen | mediumslateblue | mediumspringgreen | mediumturquoise | mediumvioletred | midnightblue | mintcream | mistyrose | moccasin | navajowhite | navy | oldlace | olive | olivedrab | orange | orangered | orchid | palegoldenrod | palegreen | paleturquoise | palevioletred | papayawhip | peachpuff | peru | pink | plum | powderblue | purple | rebeccapurple | red | rosybrown | royalblue | saddlebrown | salmon | sandybrown | seagreen | seashell | sienna | silver | skyblue | slateblue | slategray | slategrey | snow | springgreen | steelblue | tan | teal | thistle | tomato | turquoise | violet | wheat | white | whitesmoke | yellow | yellowgreen
<deprecated-system-color> = ActiveBorder | ActiveCaption | AppWorkspace | Background | ButtonFace | ButtonHighlight | ButtonShadow | ButtonText | CaptionText | GrayText | Highlight | HighlightText | InactiveBorder | InactiveCaption | InactiveCaptionText | InfoBackground | InfoText | Menu | MenuText | Scrollbar | ThreeDDarkShadow | ThreeDFace | ThreeDHighlight | ThreeDLightShadow | ThreeDShadow | Window | WindowFrame | WindowText
where 
<rgb-component> = <integer> | <percentage>
<alpha-value> = <number>
<hue> = <number>

Examples

element { 
    border-top: 1px solid #000;
}

Specifications

Specification	Status	Comment
CSS Backgrounds and Borders Module Level 3 The definition of 'border-top' in that specification.	Candidate Recommendation	No direct changes, though the modification of values for the `border-top-color` do apply to it.
CSS Level 2 (Revision 1) The definition of 'border-top' in that specification.	Recommendation	No significant changes
CSS Level 1 The definition of 'border-top' in that specification.	Recommendation	Initial definition

Browser compatibility

Feature	Chrome	Edge	Firefox (Gecko)	Internet Explorer	Opera	Safari (WebKit)
Basic support	1.0	(Yes)	1.0 (1.7 or earlier)	4	3.5	1.0 (85)

Feature	Android	Edge	Firefox Mobile (Gecko)	IE Phone	Opera Mobile	Safari Mobile
Basic support	1.0	(Yes)	1.0 (1.0)	(Yes)	(Yes)	(Yes)

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https://developer.mozilla.org/en-US/docs/Web/CSS/border-top