<div class="div-container">  
<div class="div1">1</div>  
<div class="div2">2</div>
</div>

/* 方法一 */
.div-container {  
margin: 10px 0;  
padding: 10px;  
width: 400px;  
border: 2px solid #ccc;  
position: relative;
}
.div1 {  
width: 100px;  
height: 50px;  
border: 2px solid red;
}
.div2 {  
width: 100px;  
height: 50px;  
border: 2px solid red;  
position: absolute;  
/* 边距设置 */  
right: 10px;  
top: 10px;
}

<div class="div-container2">  
<div class="div3">3</div>  
<div class="div4">4</div>
</div>

/* 方法二 */
.div-container2 {  
margin: 10px 0;  
padding: 10px;  
width: 400px;  
border: 2px solid #ccc;  
display: flex;  
justify-content: space-between;
}
.div3 {  
width: 100px;  
height: 50px;  
border: 2px solid red;
}
.div4 {  
width: 100px;  
height: 50px;  
border: 2px solid red;
}

<div class="div-container3">  
<div class="div5">5</div>  
<div class="div7">占位div</div>  
<div class="div6">6</div>
</div>

/* 方法三 */
.div-container3 {  
margin: 10px 0;  
padding: 10px;  
width: 400px;  
border: 2px solid #ccc;  
display: flex;  
justify-content: space-between;
}
.div5 {  
width: 100px;  
height: 50px;  
border: 2px solid red;
}
.div6 {  
width: 100px;  
height: 50px;  
border: 2px solid red;
}
.div7 {  
width: calc(100% - 100px - 100px);  
height: 50px;  
border: 1px solid #ccc;
}