Center multiple div blocks CSS example

code=yes

/* grebe.css 19Jun2014 */

/* ==========================================================================
   Table of Contents 
   ========================================================================== */

/*

    0.  Includes
    1.  HTML Tags
    2.  Header and Nav
    3.  Footer 
    4.  Displaying a Post
    5.  Custom CSS
        a. site-wide content display 
        b. textarea posting box
        c. text highlighting
        d. comparing posts
        e. homepage header image, title, and description area
        f. heading text
        g. small, grey text links
        h. image header for post page
        i. formatting one type of clode block
        j. submit button
        k. table of contents
        l. miscellaneous
    7.  Media Queries

 */


/* ==========================================================================
   0. Includes
   ========================================================================== */

@import url(normalize.css); 


/* ==========================================================================
   1. HTML - Defining some standard markup commands
   ========================================================================== */

html {
    height: 100%;
    max-height: 100%;
}

body {
    height: 100%;
    max-height: 100%;
    color: #000000;
    background: #ffffff;
    font-family: "Open Sans", Arial, Helvetica, sans-serif; 
    /* font-size: 100%; */  /* ~16px */ /* this is defined in the text resizer css file */
    line-height: 1.5em;
    width: 100%;
}  

img {
    max-width: 100%;
}

textarea {
    font-family: "Open Sans", Arial, Helvetica, sans-serif;  
    font-size: 1em;
    overflow: auto;
    background: #ffffff;
    border: 1px solid #ccc; 
}

blockquote {
    margin-left: .6em;
    padding-left: 1em;
    border-left: .2em solid #ddd; 
}

table {
    font-size: .8em;
    font-family: "Open Sans", Arial, Helvetica, sans-serif; 
    color: #000000;
}

hr.shortgrey {
   border: 0; 
   height: 1px; 
   background: #ddd;
   width: 25%;
   margin-top:2em;
   margin-bottom:2em;
}


h1, h2, h3, h4, h5 {
    color: #000000;
    font-family: "Open Sans", Arial, Helvetica, sans-serif; 
}

h1 {
    padding: 0;
    margin: 0;
    font-size: 1.6em;
}

h2 {
    font-size: 1.5em; 
}

h3 {
    font-size: 1.4em; 
}

h4 {
    font-size: 1.3em; 
}

h5 {
    font-size: 1.2em; 
}

h2, h3, h4, h5 {
    margin: 50px 0 10px 0;
    padding: 0;
}

a {
    text-decoration: none; 
    color: #0000ff;
}

a:visited {
    color: #cc3399;
} 

a:hover {
    text-decoration: underline;
}

a:active {
    text-decoration: underline; 
    color: #ff0000;
}

/* ol formatting adapted from: 
   http://www.456bereastreet.com/archive/201105/styling_ordered_list_numbers/ 
*/
ol {
    counter-reset: li; /* Initiate a counter */
    margin-left: 0; /* Remove the default left margin */
    padding-left: 0; /* Remove the default left padding */
}

ol > li {
    position: relative; /* Create a positioning context */
    margin: 0 0 6px 2em; /* Give each list item a left margin to make room for the numbers */
    padding: 4px 8px; /* Add some spacing around the content */
    list-style: none; /* Disable the normal item numbering */
}

ol > li:before {
    content: counter(li) ". "; /* Use the counter as content */
    counter-increment: li; /* Increment the counter by 1 */
    /* Position and style the number */
    position: absolute;
    top: -2px;
    left: -2em;
    width: 2em;
    /* Some space between the number and the content in browsers that support
       generated content but not positioning it (Camino 2 is one example) */
    margin-right: 8px;
    padding: 4px;
    font-weight: bold;
    text-align: center;
}

/* 3may2013 I think it's suppose to be ol not ul  li ul {margin-top:6px;} */
li ol {
    margin-top: 6px;
} 

ol ol li:last-child {
    margin-bottom: 0;
}

input {
    -moz-border-radius: 4px;
    -webkit-border-radius: 4px;
    border-radius: 4px; 
    border: 1px solid #cccccc;
    padding-left: .4em;
}


/* ==========================================================================
   2. Header and Nav Tag Definitions
   ========================================================================== */

header nav ul {
    list-style-type: none;
    padding: 0 0 0 0; 
    margin: 0 0 0 0;
}

header nav ul li {
    display: inline-block; 
}

header nav ul li a {
    text-align: left;
    padding: 0 .5em;
}

header {
/*    border: 1px solid #cccccc;  */
    text-align: left;
    top: 0;
    left: 0;
    display: block;
    z-index: 100; 
    float: left;
    width: 100%;
    left: auto;
    position: absolute;
    height: 20px;
}

header a {
    color: #666666;
    text-decoration: none;
}

header a:visited {
    color: #666666;
    text-decoration: none;
}

header a:hover {
    color: #666666;
    text-decoration: underline;
}


/* ==========================================================================
   3. Footer
   ========================================================================== */

footer ul {
    list-style-type: none;
    padding: 0 0 0 0; 
    margin: 0 0 0 0;
}

footer ul li {
    display: inline-block; 
}

footer ul li a {
    text-align: left;
    padding: 0 .5em;
}

footer {
    clear: right;
    clear: left;
    font-size: .9em;
    text-align: center;
    padding-bottom: 25px;
}


/* ==========================================================================
   4. Post - Formatting the main part of an article and a stream of posts
   ========================================================================== */

.largescreens-note {
    font-size: 90%;    
    line-height: 1.2em;
}

.largescreens-article {
 /*   display: none; */
}

.post {
    color: #000000;
    font-size: 130%;
    line-height: 1.7em;
}

.post, .stream-content ul > li {
    padding: 4px; /* Add some spacing around the content */
}

/* for the h1 title on the article page */
#post-top {
    padding-top: 20px;  
}

#homepage-content {
    display: -webkit-box;
    display: -moz-box;
    display: -ms-flexbox;
    display: -webkit-flex;
    display: flex;
    -webkit-box-direction: normal;
    -moz-box-direction: normal;
    -webkit-box-orient: horizontal;
    -moz-box-orient: horizontal;
    -webkit-flex-direction: row;
    -ms-flex-direction: row;
    flex-direction: row;
    -webkit-flex-wrap: wrap;
    -ms-flex-wrap: wrap;
    flex-wrap: wrap;

    justify-content: center;

/*
    -webkit-box-pack: center;
    -moz-box-pack: center;
    -webkit-justify-content: center;
    -ms-flex-pack: center;
    -webkit-box-align: center;
    -moz-box-align: center;
    -webkit-align-items: center;
    -ms-flex-align: center;
    align-items: center;
*/
}

/* on the stream page that show parts of a post/article */
.post-stream {
    font-size: 130%;
    line-height: 1.7em;
    padding: 20px;
    width: 550px;

    height: 100%;
 /*   border: 1px solid #dddddd;  */
}

.post-stream.one {
    background: #ffffff;
    color: #333;
}
.post-stream.two {
    background: #16a5d7;
background: #b3e5fc;
    color: #fff;
color: #333;
}
.post-stream.three {
    background: #ffffff;
    color: #333;
}
.post-stream.four {
/*    background: #15d657; green */
    background: #f2f2f2;
    color: #333;
}
.post-stream.five {
    background: #fff;
    color: #333;
}
.post-stream.six {
    background: #fff176;
background: #fff59d;
    color: #333;
}
.post-stream.seven {
    background: #fff;
    color: #333;
}
.post-stream.eight {
    background: #c5e1a5;
    color: #333;
}

.post-stream h1 {
    text-align: center; 
}

.jr {
    background-color: #fff;
}

.post-stream h1 {
     font-size: 1.1em; 
    /* font-size: 1.6em; */
}

.post big, em {
    font-family: "Open Sans", Arial, Helvetica, sans-serif; 
}

.post big {
    color: #666;
}

.post strong {
    color: #000000;
}

.post b {
    background: #ffff00;
    font-weight: normal;
}

.post a strong {
    color: #0000ff;
}

.post a:visited strong {
    color: #cc3399;
}

.post a:hover strong {
    text-decoration: underline;
}

.post a:active strong {
    text-decoration: underline; color: #ff0000;
}

.post code {
    font-size:13px;
    background: #f8f8f8;
    padding: 2px 5px 2px 5px;
    border: 1px solid #dddddd;
}

.post pre {
    line-height: 1em; 
    background: #f8f8f8;
}

.post pre code {
    padding:0;
    border:none;
}

/* ==========================================================================
   5. Additional Custom CSS
   ========================================================================== */

/* a. site-wide responsive content display.
   used within a section tag that defines the main viewing of the site, 
   and it's used sitewide as a responsive wrapper to make content scale. */
#content {
    position: relative;
    width:80%;
    max-width: 700px;
    margin: 0px auto 0px;
}

/* b. textarea posting box */
#textareaboxpost {
    width: 90%
    height: 250px;
}

/* c. highlighted text - used with the custom q. q.. commands for quoting other text. */
.highlighted {
    margin: .5em; 
    background: #f5faff;
    padding: 0 .5em 0 .5em;  
    border: 1px solid #cccccc;
}

/* d. next three elements are used when comparing two versions of a post */
.added {
    background-color: #cff;
}

.removed {
    background-color: #fcc;
}

.changed {
    background-color: #ff6;
}

/* e. CSS to control the image header area of the home page */
/* Big cover image on the home page */

/* tint the image. */
#site-head:before {
    position: absolute;
    top: 0;
    left: 0;
/*    background-color: rgba(0,0,0,0.2);  */
/*    background-color: rgba(169,64,198,0.2); */ /* purple A940C6 */
/*    background-color: rgba(221,221,221,0.2); */  /* light to medium grey */
    background-color: rgba(102,102,102,0.2);     /* med to dark grey */
/*    background-color: rgba(22,165,215,0.2);     */
    text-indent: -9999em;
    width: 100%;
    height: 100%;
    content: "";
    z-index: 1;
}

#site-head {
    position: relative;
    display: table;
    width: 100%;
    text-align: center;
    color: #ffffff;
    background: #000000 no-repeat center center; 
    background-size: cover;
    background-position: center;
    height: 40%;
    /* height: 60%;  see NOTE above to make this work */
/*
    padding-top: 1em;  
    padding-bottom: 1em;
*/

    /* if using a banner image on the homepage, and if want to 
       fade or lighten the image (whiteish), then use the opacity commans.
    */
    /* opacity: 0.5; */
    /* filter:alpha(opacity=50); */ /* For IE8 and earlier */
}

#blog-author-image {
    width:50px;
    height:50px;
    border-radius: 25px;
    -moz-border-radius: 25px;
    -khtml-border-radius: 25px;
    -webkit-border-radius: 25px;
}

#blog-title {
    font-size: 3em;
    line-height: 1.5em; 
    /* make the title stand out more */
    font-weight: bold; 
/*
    text-shadow: 2px 2px #000000; 
    -moz-text-shadow: 2px 2px 2px #000000;
    -webkit-text-shadow: 2px 2px 2px #000000;
    filter: dropshadow(color=#000000, offx=2, offy=2);
*/
    display: block;
}

#blog-title a {
    text-decoration: none;
}

#blog-title a:visited {
    text-decoration: none;
}

#blog-description {
    font-size: 1.2em;
    line-height: 1.5em; 
    margin-bottom: 20px; 
    /* make the description stand out more */
/*
    text-shadow: 2px 2px #000000; 
    -moz-text-shadow: 2px 2px 2px #000000;
    -webkit-text-shadow: 2px 2px 2px #000000;
    filter: dropshadow(color=#000000, offx=2, offy=2);
*/
    display: block;
}

#blog-title, #blog-title a, #blog-title a:visited, #blog-description {
    color: #fff;
} 

/* f. heading text - used for the h1, h2, h3, etc tags */
.headingtext a {
    color: #000000;
    text-decoration: none;
}

.headingtext a:visited {
    color: #000000;
    text-decoration: none;
}

.headingtext a:hover {
    color: #000000;
    text-decoration: underline;
}

.headingtext-white a {
    color: #fff;
    text-decoration: none;
}

.headingtext-white a:visited {
    color: #fff;
    text-decoration: none;
}

.headingtext-white a:hover {
    color: #fff;
    text-decoration: underline;
}

.grebe-article {
    text-indent: -9999px;
    visibility: hidden;
    display: none;
}

/* g. small, grey-colored text links */
.greytext {
    font-size: 80%;
    font-family: "Open Sans", Arial, Helvetica, sans-serif; 
}

.greytext a {
    color: #888888;
}

.greytext a:visited {
    color: #888888;
}

.greytext a:hover {
    color: #000000; 
    text-decoration: underline;
}

.lightgreytext {
    font-size: 80%;
    font-family: "Open Sans", Arial, Helvetica, sans-serif; 
}

.lightgreytext a {
    color: #ccc;
}

.lightgreytext a:visited {
    color: #ccc;
}

.lightgreytext a:hover {
    color: #fff; 
    text-decoration: underline;
}

/* h. image header for post page */

.xstream-imageheader:before {
    position: absolute;
    top: 0;
    left: 0;
    background-color: rgba(0,0,0,0.2);
    text-indent: -9999em;
    width: 100%;
    height: 100%;
    content: "";
    z-index: 1;
}

.stream-imageheader {

/*    border: 1px solid green; */

    height: 300px;
    margin: 0 auto 20px auto; 
    overflow: hidden;
    max-width: 700px;
    background: gray;
}

.stream-imageheader .inner {
    display: block;
    width: 100%;
    height: 100%;
    background-color: transparent;
    background-repeat: no-repeat;
    background-position: center center;
    background-size: cover;
}

.stream-imageheader img {
    display: block;
    max-width: 100%;
    visibility: hidden
}

/* tint the image */
#largeimageheader:before {
    position: absolute;
    top: 0;
    left: 0;
    background-color: rgba(0,0,0,0.3);
    text-indent: -9999em;
    width: 100%;
    height: 100%;
    content: "";
    z-index: 1;
}

#largeimageheader {
    position: relative;
    display: table;
    width: 100%;
    height: 60%;
    background: #000000 no-repeat center center; 
    background-size: cover;
    text-align: center;
    color: #ffffff;
}


.codeClass pre {
    white-space: pre;
}

.fenceClass pre {
    white-space: pre;
}

 /*  http://stackoverflow.com/questions/2295766/how-to-create-a-scrollable-div-tag-vertically-supported-in-chrome */
.codeClass {
    width: 100%;
    overflow-y: scroll;
    max-height:500px; 
    background: #f8f8f8;
    border: 1px solid #dddddd;
    padding: 2px 5px 2px 5px;
    white-space: nowrap;
}

.fenceClass {
    overflow-x: scroll;
    background: #f8f8f8;
    border: 1px solid #dddddd;
    padding: 2px 5px 2px 5px;
}

/* j. submit button */
.submitbutton {
    -moz-border-radius: 10px;
    -webkit-border-radius: 10px;
    border-radius: 10px; 
    font-size: 1em;
    color: #666;
    background: #fff;
    border: 1px solid #b8b8b8;
}

.submitbutton:hover {
    color: #000;
    border: 1px solid #222;
}

#sign-up-button {
    -moz-border-radius: 10px;
    -webkit-border-radius: 10px;
    border-radius: 10px; 
    color: #FAFAFA;
    background: #0080FF;
    border: 1px solid #0080ff;
}

#sign-up-button:hover {
    color: #fff;
    background: #00BFFF;
    border: 1px solid #00bfff;
}

/* k. table of contents box displayed in upper right corner of a post page */
 #toc {
    font-family: "Open Sans", Arial, Helvetica, sans-serif; 
    font-size: .8em;
    float: right;
    background: #f0fff0; /* light blue */
    display: inline;
    width: 12.5em;
    text-align: left;
    border: 1px solid #cccccc;
    line-height: 1.2em;
    padding-top: .3em;
    padding-bottom: .3em;
    margin: 1.2em 0 1.2em 1.2em;
} 

.toclevel1 {
    margin-left: 0;
}

.toclevel2 {
    margin-left: .3em;
}

.toclevel3 {
    margin-left: .6em;
}

.toclevel4 {
    margin-left: .9em;
}

.toclevel5 {
    margin-left: 1.2em;
}

/* l. miscellaneous */

/* used in the nav area */
.userlink {
/*    background: #ffffff; using font awesome instead of plain text */
}

/* http://fortawesome.github.io/Font-Awesome/ */
.fa {
    color: #666666;
    color: #c0c0c0;
}

.fa-cog, .fa-pencil, .fa-file-text  {
    color: #3300ff;
}

.undelete {
    background: #ffff99;
    font-size: 0.6em;
}

.smallscreens {
    display: none;
}

#loggedinuserinfo {
    background: #e0eeee;
}

#olderlink {
    float: right;
}

#post-min-read {
    float:right; 
    font-size:80%; 
    margin-top:5px;
}

/* ==========================================================================
   7. Utilities from the Ghost blog Casper Theme
   ========================================================================== */
/* Hides content */
.hidden {
    text-indent: -9999px;
    visibility: hidden;
    display: none;
}
/* Creates a responsive wrapper that makes our content scale nicely */
.inner {
    position: relative;
    width: 80%;
    max-width: 700px;
    margin: 0 auto;
}
/* Centres vertically. (IE8+) */
.vertical {
    display: table-cell;
    vertical-align: middle;

/* if want the text on the image to be tinted too, then comment out these two lines.
   these two lines will make the the text color be what's defined in site-head, blog-title, or blog-description.
*/
    z-index: 10; 
    position: relative;
}




/* ==========================================================================
   7. Media Queries
   ========================================================================== */

/*
  desktop/laptop > 1224px 
  tablet 768-1024px 
  smartphone 320-480px  
*/

/* 45em = 720 px */
@media only screen and (max-width: 45em) { 
    #content {
        width: 90%;
    }
    .stream-content {
        width: 95%;
    }
}

/* 37.5em = 600px */
@media only screen and (max-width: 37.5em) {
    .stream-imageheader {
        height: 240px;
    }

    .post-stream h1 {
        font-size: 1.1em;
    }

    #site-head {
        height: 20%;
    }

    #largeimageheader {
        padding-top: 65%;
        height: auto;
    }

    .post, .post-stream {
        /* font-size: 1.15em; commented out on 2-Oct-2014 */
        /* line-height: 1.4em; commented out on 2-Oct-2014 */
        font-size: 125%; /* increases the font size when viewed on a small screen */
    }

    #blog-description {
        font-size: 1em;
    }

    #toc {
        display: none;
    }

    /* .homepage-post-author, .homepage-post-date */
    .largescreens-article, .largescreens-draft, .homepage-min-read,  .homepage-tagstring, #post-min-read {
        display: none; /* commented out for testing on 19jun2014 */
    }

    .post-stream {
        padding: 10px 0 10px 0; 
    }

    .smallscreens {
        display: inline;
    }

    h1 {
        font-size: 1.40em;
    }

    h2 {
        font-size: 1.30em; 
        /* padding-top: .2em; */
    }

    h3 {
        font-size: 1.20em; 
    }

    h4 {
        font-size: 1.15em; 
    }

    h5 {
        font-size: 1.10em; 
    }

    #microblogtextareabox {
        width: 85%;
    }   

    footer ul li a {
        padding: 0 .3em;
    }

    #blog-title {
        font-size: 1.8em;
    }

}

@media only screen and (max-width: 480px) { 
    .stream-imageheader {
        height: 180px;
    }
}

@media only screen and (min-width: 320px) { 
    #textareaboxpost {
        width: 95%;
        height: 125px;
    }

    .post {
        color: #222222;
    }

    #blog-title, #blog-title a, #blog-title a:visited, #blog-description {
    } 
}

@media only screen and (max-width: 320px) { 
    .stream-imageheader {
        height: 100px;
    }

    #scroll_text {
        width: 100%;
        height: 700px;
        overflow-y: auto; 
        -webkit-overflow-scrolling: touch;
    }
    #blog-title {
        font-size: 1.5em;
    }
}

@media only screen and (min-width: 768px) {
    #textareaboxpost {
        width: 90%;
        height: 200px;
    }
}

@media only screen and (min-width: 1025px) {
    #textareaboxpost {
        width: 90%;
        height: 250px;
    }
}

@media only screen and (max-width: 900px) {
    #content {
        padding-top: 10px;
    }
}

/* 76.5em = 1224 px */
@media only screen and (min-width: 76.5em) { 
/* use if font-size = 125% 
    .post {
        color: #333333;
    }
*/

    .post p {
        margin-top: 25px;
        margin-bottom: 25px;
    }
}    




/* ==========================================================================
   End grebe.css
   ========================================================================== */