question 1: the combined class selector selects the node behind it, so how do you choose the previous one?
    <a href="https://segmentfault.com" class="p1">This is a paragraph.1</a>
    <a href="https://segmentfault.com" class="p2">This is a paragraph.2</a>
.p1:hover+.p2 {
                outline: 10px double purple;
            }
            
.p2:hover~.p1 {
                outline: 10px double purple;
            } actually want to do is: mouse hover p1, give p2 a box; mouse hover p2, give p1 a box. However, the second half of the sentence is invalid. 
 tried  combination selector . They all select nodes backward and cannot move forward.? 
 question 2: how do I select two or more elements with different parents? 
 is still the example above. The HTML I started with is written like this 
<div>    
    
        <a href="https://segmentfault.com" class="p1">This is a paragraph.1</a>
    
    
        <a href="https://segmentfault.com" class="p2">This is a paragraph.2</a>
    
</div> later found that the combination choices are all   above, which seems to have nothing to do with it. How can I achieve the purpose of question 1?  brothers   descendants , like  which belongs to two 
