Check out example codes for "css block". It will help you in understanding the concepts better.

Code Example 1

/******************* BASIC BLOCK POSITIONING **********************/

/******************** Static Position  *************************/
/*All elements are static in their position by default. Which means 
that, all elements are organized just like they would if your code 
didn't have any CSS and were just pure HTML */

tag_name {
  position: static;
}

/******************** Relative Position *************************/
/*It allow us to position this element relative to how it would have
been positioned had it been static. You can use the coordinate 
properties to guide this element (by giving some margins to the block), 
relative to what was the standard layout. This new position will not 
influence the distribution of other elements (the others will keep 
the standard layout, as if your element leaves a "shadow" of where it 
was supposed to be). Therefore, some overlaps and lack of coordination 
can occur when you move your element*/

tag_name {
  position: relative;
  left: 30px;
  right: 10px;
  bottom: 2px;
  top: 4px;
  
  z-index: 1;  /* It decides which element will show on top of the 
                  other. The first to show, is the one with the 
                  greatest index */
}

/******************** Absolute Position *************************/
/* With this property, we are able to position the element relative 
to the <body> or relative to it's parent, IF the parent is itself isn't 
"static". Using the coordination properties, we do not increase or 
decrease the margins in relation to the standard position, but rather, 
we are increasing or decreasing the distance in relation to the "walls" 
of the block that contains this element, for example, a parent <div> 
that contains a <h1> element. The name "absolut", comes from the cases 
where the parent is the <body> element. When you use this property, 
you are taking the element away from the natural flow of your document, 
so, the other elements position will not take into account your absolute 
element*/

tag_name {
  position: absolute;
  left: 30px;
  right: 10px;
  bottom: 2px;
  top: 4px;  
  
  z-index: 1;  /* It decides which element will show on top of the 
                  other. The first to show, is the one with the 
                  greatest index */
}

/* For exemple: */

div{
  position: relative;
}

h1 {
  position: absolute;      /* In relation to the div element*/
  left: 30px;
  top: 4px;
}

/******************** Fixed Position *************************/
/*As soon as the element is fixed in a certain position, relative 
to it's parent, then, whenever we scroll down the webpage, the element 
maintains its fixed position on the screen. This property will also 
make the other html elements, ignore the position of this element 
during their layout (it takes it away from the natural flow of the 
document). */

tag_name {
  position: fixed;
  left: 30px;
  right: 10px;
  bottom: 2px;
  top: 4px;
  
  z-index: 2;  /* It decides which element will show on top of the 
                  other. The first to show, is the one with the 
                  greatest index */
}

/******************** Sticky Position *************************/
/* This property will stick the element to the screen when you 
reach its scroll position */

tag_name {
  position: -webkit-sticky;   /* For Safari */
  position: sticky;
  left: 20px;
  right: 60px;
  bottom: 5px;
  top: 13px;
  
}

/******************* NOTES ABOUT THE Z-INDEX **********************/
/* By default, the z-index of an element is zero, so if you change the 
z-index to something above or below that value, you are putting that 
element above or below the ones you didn't change.
Another important thing to be aware of is that the z-index only worked 
for elements that have a position different from the standard. This 
means that, for elements with Static position, this won't work.
So, you can only make two elements interact in the z plane if they both 
have a define position as: Relative, Absolute, Fixed, ... */

tag_name_1 {
  position: absolute;
  z-index: -1;
  
}

tag_name_2 {
  position: relative;      /* tag_name_1 will be below the tag_name_2 */
}

Code Example 2

/******************* BASIC BLOCK DISPLAY **********************/

/**************** Block display Elements  *********************/
/*Elements that block any other elements from being in the 
same line. You can change the width from being the maximum 
width of the page, but you can´t put elements side by side */
tag_name {
    display: block;
}

/*Exemple of default block display elements:*/
<h1> ... </h1>
<p> ... </p>


/**************** Inline display Elements  *********************/
/*They are the type of blocks that only take up the minimum space 
required (both in width and height). You can place these types of 
blocks side by side (on the same line) but you cannot change their 
dimensions */

tag_name {
    display: inline;
}

/*Exemple of default inline display elements:*/
<spans> ... </spans>
<img> ... </img>
<a> ... </a>


/************* Inline-block display Elements  *****************/
/*They take the best of the two other types above. You can put 
elements side by side (on the same line) and you can change this 
block width and height */

tag_name {
    display: inline-block;
}


/***************** None display Elements  ********************/
/*This block will never appear on your webpage and will never 
interact with the other elements (it doesn't take up space) */

tag_name {
    display: none;
}

Code Example 3

display:inline;

Code Example 4

span.a {
  display: inline; /* the default for span */
  
  width: 100px;
  height: 100px;
  
  padding: 5px;
  border: 1px solid blue; 
  background-color: yellow; 
}

span.b {

    display: 
  inline-block;
  width: 100px;
  height: 
  100px;
  padding: 5px;
  border: 1px 
  solid blue; 
  background-color: yellow; 
}


  span.c {
  display: block;
  width: 
  100px;
  height: 100px;
  padding: 5px;
  
  border: 1px solid blue; 
  background-color: yellow; 
}

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