Browser bookmarklet "UnCSS" improves readability of long texts by replacing all original styles with better line-heights, font sizes, paragraph margins, few colors etc. Firefox provides this out of the box (Reader Mode). The Brave-browser, however, does not.

bookmarklet-uncss.js

javascript: (function() {
	
	const DARKMODE = true;
	
	
	function every( sel, how, fil )	{
		Array.from( document.getElementsByTagName( sel ))
			.filter( e => fil ? fil( e ) : true )
			.forEach( how );
	}

	function hasPrevText( e ) {
		while( e = e.previousSibling )
			if( e.nodeType != Node.COMMENT_NODE ) return true;
		return false;
	}

	function rmAtts( e ) {
		while( e.attributes.length > 0 ) e.removeAttribute( e.attributes[0].name );
	}
	
	const styled = s => e => e.style.cssText = s;
	const hcss   = 'line-height: 1.25em; font-size:';
	every( 'body',  rmAtts );	
	every( 'font',  rmAtts );
	every( 'table', rmAtts );
	every( 'td',    rmAtts );
	Array.from( document.styleSheets ).forEach( s => s.disabled = true );
	every( '*',  styled( 'line-height: inherit; font-size: inherit; padding: 0; margin: 2em 0 1em 0;' ));
	every( 'a',  styled( DARKMODE ? 'color: #68a6c3;' : 'color: #1079ab' ));
	every( 'li', styled( 'margin: 0.25em 0;' ));
	every( 'h1', styled( hcss + '1.7em;' ));
	every( 'h2', styled( hcss + '1.5em;' ));
	every( 'h3', styled( hcss + '1.2em;' ));
	every( 'h4', styled( hcss + '1.1em;' ));
	every( 'br', e => e.insertAdjacentHTML( 'afterend', '<br>' ), e => hasPrevText( e ));
	document.body.style.cssText = 'margin: 2em auto 5em auto; width: 800px; min-width: 0; max-width: 800px; font-size: 16pt; line-height: 1.5em;' +
		(DARKMODE ? 'background-color: #131516; color: #CECAC3'
		          : 'background-color: #efefef; color: #000');
})();