Does not look consistent to some other parts of HA - but since you asked…
customElements.whenDefined('ha-config-device-page').then(() => {
const DevicePage = customElements.get('ha-config-device-page');
const { html, css } = DevicePage.prototype;
const newStyle = css`
hass-subpage > .container {
max-width: none;}`;
const newStyles = [].concat(DevicePage.styles, newStyle);
Object.defineProperty(DevicePage, 'styles', {value: newStyles, configurable: true, enumerable: false});
Object.defineProperty(DevicePage, 'elementStyles', {value: newStyles, configurable: true, enumerable: false});
});
frontend:
extra_module_url:
- /local/js-extenstions/test/device_page_wide.js
