在类中选择一个类并使其具有自己的行

Question

如何在课堂上选择课程？ CSS

需要做的事情：在“按钮”中选择“fourthRow”并使类出现在它自己的行上另外，如果有人知道如何使这个代码更有效，那将非常感激。非常湿的代码。

<!DOCTYPE html>
    <html>
    <head>
    	<title>Calculator</title>
    	<link rel="stylesheet" type="text/css" href="style.css">
    </head>
    <body>
    <div class="buttons">
    	<div class="fourthRow">
    		<div>
    			<button class="7">7</button>
    		</div>
    		<div>
    			<button class="8">8</button>
    		</div>
    		<div>
    			<button class="9">9</button>
    		</div>
    		<div>
    			<button class="divide">&#247;</button>
    		</div>
    	</div>
    	<div class="thirdRow">
    		<div>
    			<button class="4">4</button>
    		</div>
    		<div>
    			<button class="5">5</button>
    		</div>
    		<div>
    			<button class="6">6</button>
    		</div>
    		<div>
    			<button class="multiplicaton">x</button>
    		</div>
    	</div>
    	<div class="secondRow">
    		<div>
    			<button class="1">1</button>
    		</div>
    		<div>
    			<button class="2">2</button>
    		</div>
    		<div>
    			<button class="3">3</button>
    		</div>
    		<div>
    			<button class="subtract">-</button>
    		</div>
    	</div>
    	<div class="firstRow">
    		<div>
    			<button class="0">0</button>
    		</div>
    		<div>
    			<button class="dot">.</button>
    		</div>
    		<div>
    			<button class="equal">=</button>
    		</div>
    		<div>
    			<button class="add">+</button>
    		</div>
    	</div>
    
    </div>
    
    </body>
    </html>

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