Override @page{margin} rules with reasonable values

override-atpage-margin.js

// Override @page{margin} rule if found
var docSS = document.styleSheets, ss, ess; 
for (var i=0; i<docSS.length; i++){
	if (!docSS[i].disabled){
		// check content of style sheet for @page (type 6 style sheet)
		// https://developer.mozilla.org/en-US/docs/Web/API/CSSRule#Type_constants
		ss = docSS[i];
		for (var j=0; j<ss.cssRules.length; j++){
			if (ss.cssRules[j].type == 6){ // Page sheet
				if (ss.cssRules[j].cssText.indexOf('margin') > -1){
					// Try overriding to 0.5in top/bottom, 0.25in left/right
					ss.cssRules[j].style.margin = '1.27cm 0.64cm';
				}
			} else if (ss.cssRules[j].type == 4){ // Print Media sheet
				// Check for any embedded Page sheet inside
				ess = ss.cssRules[j];
				for (var k=0; k<ess.cssRules.length; k++){
					if (ess.cssRules[k].type == 6){
						if (ess.cssRules[k].cssText.indexOf('margin') > -1){
							// Try overriding to 0.5in top/bottom, 0.25in left/right
							ess.cssRules[k].style.margin = '1.27cm 0.64cm';
						}
					}
				}
			}
		}
	}
}