JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">
     <div class="aside_left">Left content...</div>
     <div class="main_page">Main content...</div>
</div> <!-- end of wrapper -->
<div class="wrapper">
     <div class="aside_left">Left content...</div>
     <div>Some content...</div>
     <div>More content...</div>
</div> <!-- end of wrapper -->

CSS

/* your typical css */
.wrapper > .aside_left,
.wrapper > div {
    float:left;
}
.wrapper {clear: both;}

.wrapper > .aside_left:nth-last-of-type(2) {
    float: right;
}