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Fixed inner divs on scrollable outer

I have some page content in a React web app where certain fields should remain fixed as the user scrolls. The part that's throwing me off is this content is contained within a scrollable outer div. That outer div must remain scrollable because it occasionally loads different components that need it.
Here is the div structure:
<div class="inner"><!-- overflow-y: auto; (this must remain)-->
<div class="wrapper">
<div class="titleBar"> <!-- I need this to not scroll -->
<div class="mainTable">
<table>
<th>...</th> <!-- I need this to not scroll -->
<tbody>
...
</tbody>
</table>
</div>
</div>
</div>
</div>
So as the user scrolls down the page, the title bar and table header should remain fixed, with the table body content being the only thing on the page that is scrolling. I'm not able to just make the table body scrollable because that will put a scrollbar on the table itself, it needs to scroll on the actual page scroll.
Most posts on this I've been able to find are using JQuery, but since this is within ReactJS I'm looking for other solutions.

Correct table head structure is:
<table>
<thead>
<tr>
<th></th>
<th></th>
</tr>
</thead>
</table>
Then try customize thead th css as following:
thead th {
position:sticky;
top: 0
}

center button after change display mode

I have a problem with centering a button after I set it to display: block.
I've got a table:
<table border="0" id="contacts" width="100%">
<tr><td><div align="center"><button style="width:200px;">btn1</button></div></td></tr>
<tr><td><div align="center"><button style="width:200px;">btn1</button></div></td></tr>
</table>
Both buttons are centered in the table. Now I switch the visibility with:
document.getElementById("contacts").style.display = "none";
The table and buttons are invisible. After I switch the visibility back with:
document.getElementById("contacts").style.display = "block";
The buttons are aligned to the left. How can I center the buttons again?

First, do not use a table structure for formatting. Tables have their place, but using them as HTML scaffolding is so 1990. Instead, use DIVs with css.
Break your page up into several outer boxes, or containers. (For this, you can use DIVs - you can use DIVs for just about all containers - or sections or other container elements depending on your need for extra SEO cred.)
Within each outer container (div), you then subdivide into the type of layout you need (again, using divs). Then, within each sub-area, again use divs (or other container element) to do any further sub-divisions.
So, how to size / position all these things? Use CSS.
In css, there is a reason why the most important change from Bootstrap3 to Bootstrap4 is moving from floats to flexbox. Floats was the old way to position items; flexbox (and CSSGrid) are the new way. Flexbox is dead easy.
Flexbox requires two things:
A parent container (e.g. DIV, section, aside, p, etc)
One or more child elements (e.g. div, p, img, etc)
Here is an excellent 5min video tutorial
Here is a great cheatsheet

You would use document.getElementById("contacts").style.display = "table";

You could also give it a class "align-content-center" in this example
<table border="0" id="contacts" width="100%">
<tr>
<td>
<div class="align-content-center">
<button style="width:200px;">btn1</button>
</div>
</td>
</tr>
<tr>
<td>
<div class="align-content-center">
<button style="width:200px;">btn1</button>
</div>
</td>
</tr>
</table>
and then just style your div around the buttons
.align-content-center{
width: 100%;
text-align: center;
}

How to make whole table row clickable?

I have searched this site for a better solution on this but it seems that I can't find the right one.
I want to make my whole table row clickable in case of PC and also same thing should happen when user touches anywhere inside the row in case of tablet.
So far I have the following code and I would prefer a Html or JavaScript solution or anything along those lines.
<tr onclick="window.document.location='';">
<td><img src="/chemsolver/images/help.jpeg" alt="" width="36" height="36" id="Synthesis2" style="background-color: #996633" align="right" /></td>
<td> Help With Table </td>
</tr>

Set display: block on the anchor tag. And then set your height on the anchor.
http://jsfiddle.net/u2qLC/
Alternatively use an onclick event on the tr and have cursor: pointer set on the tr. Instead of using anchor tag.

Slide Down tabe row smoothly and Slowly

I want to Slide Down tabe row smoothly and Slowly.
The problem now is, it is instantly appearing and hiding, how can i make it smooth.
**Please check this fiddle:**
http://jsfiddle.net/5WT9g/2/
HTML:
Show Content
<br><br><br>
<table width="400" border="1">
<tr id="mainContent" style="display:none;">
<td> THIS IS MAIN CONTENT </td>
</tr>
</table>
JS:
$('#showContent').click(function ()
{
$('#mainContent').slideToggle('slow');
});

I think you mean to use slideToggle() and not toggleslide().
However, the animation still won't work smoothly for table cells. It will work slightly more smoothly if you set a height for the tr. For a completely smooth animation, I recommend using divs instead.
Here is a modified version of your code that has a sort of smooth animation with tables:
http://jsfiddle.net/TS77v/1/
As you can see, you will have to do the animation on the td, not the tr. I also had to set the height of the td for this to work, otherwise it will just appear and disappear.
Why doesn't the animation work properly on tables?
From "Learning jQuery" by Chaffer and Swedberg
Table rows present particular obstacles to animation, since browsers
use different values (table-row and block) for their visible display
property. The .hide() and .show() methods, without animation, are
always safe to use with table rows. As of jQuery version 1.1.3,
.fadeIn() and .fadeOut() can be used as well.
For your reference: https://stackoverflow.com/a/920480/3016565

It would be much easier with divs but if you prefer/need tables then tables it is. I'd do it by putting a div inside the table cell ja use the slideToggle to it. Yes, it still adds the div there but atleast you got the table structure. To make it work you need to do just a minor change to your HTML code, JS stays the same:
HTML
Show Content
<br><br><br>
<table width="400" border="1">
<tr>
<td><div style="display: none;" id="mainContent">THIS IS MAIN CONTENT</div></td>
</tr>
</table>
And a fiddle: http://jsfiddle.net/32HR9/1/
AFTER GETTING THE INFORMATION THAT YOU CAN'T CHANGE THE HTML
I assume you can edit the javascript? You haven't said anything about that. This trick isn't neat but there's no need to change the HTML and it gets the job done:
So, with jQuery
Make the tr visible.
Wrap the content of the tr in a div.
Hide the div.
Make the slideToggle work with the created div.
with code
$('#mainContent').css('display', 'table-row');
$('#mainContent > td').wrapInner("<div class='hideshow'></div>");
$('.hideshow').css('display', 'none');
$('#showContent').click(function (){
$('.hideshow').slideToggle('slow');
});
and a fiddle: http://jsfiddle.net/5E5VS/7/

Try this.
Show Content
<table id="mainContent" width="400" border="1">
<tr>
<td> <p style="display: none"> THIS IS MAIN CONTENT</p></td>
</tr>
</table>
$("#showContent").click(function () {
$('#mainContent').find("p").slideToggle();
});

fixed headers in table, html

i had an table like this
<div style="overflow:auto">
<table>
<thead><tr style="position:fixed"><th></th></tr></thead>
</table>
</div>
Now my problem is when i scroll div the header(that is tr element) is fixed it works fine but when i scroll the scrollbar of window the header tr is not fixed inside the div. I moves along the scroll bar of the window... Can any one help me to find out the solution please

I don't know If I'm getting your question right, but you may find this helpful http://fixedheadertable.com/

Sorry, I tried to do it in CSS alone, but that didn't work out, so you do need a bit of Javascript.
<div style="overflow:auto; position:relative;"
onscroll="document.getElementById('fixedtr').style.top = this.scrollTop+'px';">
<table>
<thead>
<tr style="position:absolute; top:0; left:0" id="fixedtr">
<th>Table header</th>
</tr>
</thead>
See jsFiddle.
This is how you want it, right?