Even though CSS syntax is case-insensitive (except for variables), sharing some style conventions is a key point to make it possible for a team to efficiently collaborate.

This rule checks that all the following elements are written in lower case:

Noncompliant Code Example

@CHARSET "UTF-8"; /* Noncompliant CHARSET @-rule keyword */

.mybox {
  COLOR: blue; /* Noncompliant COLOR property*/
}

.mybox {
  color: RGB(255,255,255); /* Noncompliant RGB function */
}

A:hover {} /* Noncompliant A type selector */

a:HOVER {} /* Noncompliant HOVER pseudo identifier */

*:NOT(foo) {} /* Noncompliant NOT pseudo function */

.mybox {
  width: 10PX; /* Noncompliant PX unit */
  color: #FFFFFF; /* Noncompliant #FFFFFF hexadecimal value */
}

Compliant Solution

@charset "UTF-8";

.mybox {
  color: blue;
}

.mybox {
  color: rgb(255,255,255);
}

a:hover {}

*:not(foo) {}


.mybox {
  width: 10px;
  color: #ffffff;
}

Exceptions

SCSS interpolated properties are not checked for lowercase. For instance, the following piece of code does not raise any issue: 

.mybox {
  #{$BG}-color: green;
}

The following functions can be either written in lowercase or as follow:

Alpha BasicImage BlendTrans
Blur Chroma Compositor
DropShadow Emboss Engrave
FlipH FlipV Glow
Gray ICMFilter Invert
Light MaskFilter Matrix
MotionBlur progid:DXImageTransform.Microsoft.AlphaImageLoader progid:DXImageTransform.Microsoft.Barn
progid:DXImageTransform.Microsoft.BasicImage progid:DXImageTransform.Microsoft.BblendTrans progid:DXImageTransform.Microsoft.Blinds
progid:DXImageTransform.Microsoft.Blur progid:DXImageTransform.Microsoft.CheckerBoard progid:DXImageTransform.Microsoft.Chroma
progid:DXImageTransform.Microsoft.Compositor progid:DXImageTransform.Microsoft.DropShadow progid:DXImageTransform.Microsoft.Emboss
progid:DXImageTransform.Microsoft.Engrave progid:DXImageTransform.Microsoft.Fade progid:DXImageTransform.Microsoft.FlipH
progid:DXImageTransform.Microsoft.FlipV progid:DXImageTransform.Microsoft.Glow progid:DXImageTransform.Microsoft.Gradient
progid:DXImageTransform.Microsoft.GradientWipe progid:DXImageTransform.Microsoft.Gray progid:DXImageTransform.Microsoft.ICMFilter
progid:DXImageTransform.Microsoft.Inset progid:DXImageTransform.Microsoft.Invert progid:DXImageTransform.Microsoft.Iris
progid:DXImageTransform.Microsoft.Light progid:DXImageTransform.Microsoft.MaskFilter progid:DXImageTransform.Microsoft.Matrix
progid:DXImageTransform.Microsoft.Motionblur progid:DXImageTransform.Microsoft.Pixelate progid:DXImageTransform.Microsoft.RadialWipe
progid:DXImageTransform.Microsoft.RandomBars progid:DXImageTransform.Microsoft.RandomDissolve progid:DXImageTransform.Microsoft.Redirect
progid:DXImageTransform.Microsoft.RevealTrans progid:DXImageTransform.Microsoft.Shadow progid:DXImageTransform.Microsoft.Side
progid:DXImageTransform.Microsoft.Spiral progid:DXImageTransform.Microsoft.Stretch progid:DXImageTransform.Microsoft.Strips
progid:DXImageTransform.Microsoft.Wave progid:DXImageTransform.Microsoft.Wheel progid:DXImageTransform.Microsoft.Xray
progid:DXImageTransform.Microsoft.Zigzag Redirect RevealTrans
rotateX rotateY rotateZ
scaleX scaleY scaleZ
Shadow skewX skewY
snapInterval snapList translateX
translateY translateZ Wave
Xray

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