MathMLElement: style property

The read-only style property of the MathMLElement returns the inline style of an element in the form of a live CSSStyleDeclaration object that contains a list of all styles properties for that element with values assigned only for the attributes that are defined in the element's inline style attribute.

Shorthand properties are expanded. If you set style="border-top: 1px solid black", the longhand properties (border-top-color, border-top-style, and border-top-width) are set instead.

This property is read-only, meaning it is not possible to assign a CSSStyleDeclaration object to it. Nevertheless, it is possible to set an inline style by assigning a string directly to the style property. In this case the string is forwarded to CSSStyleDeclaration.cssText. Using style in this manner will completely overwrite all inline styles on the element.

Therefore, to add specific styles to an element without altering other style values, it is generally preferable to set individual properties on the CSSStyleDeclaration object. For example, you can write = "red".

A style declaration is reset by setting it to null or an empty string, e.g., = null.

Note: CSS property names are converted to JavaScript identifier with these rules:

  • If the property is made of one word, it remains as it is: height stays as is (in lowercase).
  • If the property is made of several words, separated by dashes, the dashes are removed and it is converted to camel case: background-attachment becomes backgroundAttachment.
  • The property float, being a reserved JavaScript keyword, is converted to cssFloat.

The style property has the same priority in the CSS cascade as an inline style declaration set via the style attribute.


A live CSSStyleDeclaration object.


Getting style information

The following code snippet demonstrates how the style attribute is translated into a list of entries in CSSStyleDeclaration :

<math xmlns="">
    <mo stretchy="false">(</mo>
    <mi class="parameter" style="color: red; border-bottom: 1px solid">x</mi>
    <mo stretchy="false">)</mo>
<pre id="out"></pre>
const element = document.querySelector(".parameter");
const out = document.getElementById("out");
const elementStyle =;

// We loop through all the element's styles using ``
for (const prop in elementStyle) {
  // We check if the property belongs to the CSSStyleDeclaration instance
  // We also ensure that the property is a numeric index (indicating an inline style)
  if (
    Object.hasOwn(elementStyle, prop) &&
  ) {
    out.textContent += `${
    } = '${elementStyle.getPropertyValue(elementStyle[prop])}'\n`;


CSS Object Model (CSSOM)
# dom-elementcssinlinestyle-style

Browser compatibility

BCD tables only load in the browser

See also