Honestly your question seems more oriented to css
You can truncate text, and add dots (...) using "ellipsis"
Example, if you have inside html something like:
<p class='ellipsis'>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur<p>
and you add something like this on css :
.ellipsis {
white-space: nowrap;
overflow: hidden;
text-overflow: ellipsis;
}
p.block {
width: 300px;
}
Result is something like :
<p class='ellipsis'>Lorem ipsum dolor sit amet ...</p>
If you want implement a button "read more", on click, just remove the 'ellipsis' class, and all text will be displayed.
More info there :
Ellipsis info