html - How to reduce space between my column using a div -


i want reduce space between column; see page talking @ http://mathstructure.com/add-subtract-multiply-and-divide/

users of webpage cannot see other 2 column me out please:

<div class="container">     <div class="row">         <ol class="breadcrumb">             <li><a href="/">home</a></li>             <li><a href="/flashcards">flashcards</a></li>             <li class="active">addition, subtraction, multiplication,                 division</li>         </ol>     </div>      <div class="row">         <div class="col-md-6">             <div class="row">                 <div class="mcq_cont">                     <div class="ans_not">                         <p class="upperp"></p>                         <p class="lowerp"></p>                     </div>                     <div class="ans_ok">                         <p class="upperok"></p>                         <p class="lowerok"></p>                     </div>                     <div class="question_cont_mcq shadowstyle">                         <div class="qcont_inner">                             <p class="a fibq1">9999</p>                         </div>                         <div class="qcont_inner">                             <p class="fibq2">                                 <span class="fibsign">+</span>&nbsp;&nbsp;                    <span class="b">999</span>                             </p>                         </div>                         <hr>                     </div>                     <div class="ans_mcq_cont">                         <div class="ans_mcq" id="a1"></div>                         <div class="ans_mcq" id="a2"></div>                         <div class="ans_mcq" id="a3"></div>                         <div class="ans_mcq" id="a4"></div>                     </div>                 </div>                 <div class="fib_cont">                     <div class="ans_not">                         <p class="upperp"></p>                         <p class="lowerp"></p>                     </div>                     <div class="ans_ok">                         <p class="upperok"></p>                         <p class="lowerok"></p>                     </div>                     <div class="question_cont shadowstyle">                         <div class="qcont_inner">                             <p class="a fibq1">9999</p>                         </div>                         <div class="qcont_inner">                             <p class="fibq2">                                 <span class="fibsign">+</span>&nbsp;&nbsp;      <span class="b">999</span>                             </p>                         </div>                         <hr>                     </div>                     <input type="text" class="fib_in" id="answer_input" />    <input                         type="submit" class="ans" value="answer"/>                 </div>             </div>             <div class="row">                 <div class="stat">                     <p class="statpleft">number correct :</p>                     <p class="statpright" id="stat_correct">0</p>                     <p class="statpleft">number attempted:</p>                     <p class="statpright" id="stat_attempt">0</p>                     <p class="statpleft">percentage:</p>                     <p class="statpright" id="stat_percent">33</p>                     <p class="statpleft final_content" id="final_message"></p>                     <p class="statpright final_content" id="stat_percent">                         <input type="submit" class="restart" value="restart" />                     </p>                 </div>             </div>             </div>         <div class="col-md-6">             <div class="row">                 <div class="col-xs-6">                     <div class="option_cont">                         <p class="heading_option">problem type</p>                         <div class="options op1">                             <input type="radio" id="gtype1" name="gtype" checked /><label                             for="gtype1"> addition</label>                         </div>                         <div class="options op2">                             <input type="radio" id="gtype2" name="gtype" /><label                             for="gtype2"> subtraction</label>                         </div>                         <div class="options op1">                             <input type="radio" id="gtype3" name="gtype" /><label                             for="gtype3"> multiplication</label>                         </div>                         <div class="options op2">                             <input type="radio" id="gtype4" name="gtype" /><label                             for="gtype4"> division</label>                         </div>                     </div>                 </div>                 <div class="col-xs-6">                     <div class="option_cont">                         <p class="heading_option">difficulty</p>                         <div class="options op1">                             <input type="radio" id="difficult1" name="difficult" checked /><label                             for="difficult1"> easy (0-8)</label>                         </div>                         <div class="options op2">                             <input type="radio" id="difficult2" name="difficult" /><label                             for="difficult2"> medium (1-12)</label>                         </div>                         <div class="options op1">                             <input type="radio" id="difficult3" name="difficult" /><label                                 for="difficult3"> hard (1-18)</label>                         </div>                         <div class="options op1">                             <input type="radio" id="difficult4" name="difficult" /><label                                 for="difficult4"> expert (1-100)</label>                         </div>                     </div>                 </div>             </div>             <div class="row">                 <div class="col-xs-6">                     <div class="option_cont">                         <p class="heading_option">answer type</p>                         <div class="options op1">                             <input type="radio" id="atype2" name="atype"/><label                                 for="atype2"> multiple choice</label>                         </div>                         <div class="options op2">                             <input type="radio" id="atype1" name="atype" checked/><label                              for="atype1"> fill in blank</label>                         </div>                     </div>                 </div>                 <div class="col-xs-6">                     <div class="option_cont">                        <p class="heading_option">number entry</p>                        <div class="options op1">                           <input type="radio" id="numberentrynormal" name="numberentry"                              checked /><label for="numberentrynormal"> normal</label>                        </div>                        <div class="options op2">                           <input type="radio" id="numberentryrighttoleft" name="numberentry" /><label                              for="numberentryrighttoleft"> right left</label>                        </div>                     </div>                 </div>             </div>             <div class="row">                 <div class="col-xs-6">                     <div class="option_cont">                         <p class="heading_option">math fact</p>                         <div class="options">                           <select id="math_fact_select">                              <option value="random" selected>random                              <option value="0">0                              <option value="1">1                              <option value="2">2                              <option value="3">3                              <option value="4">4                              <option value="5">5                              <option value="6">6                              <option value="7">7                              <option value="8">8                              <option value="9">9                              <option value="10">10                              <option value="11">11                              <option value="12">12                              <option value="13">13                              <option value="14">14                              <option value="15">15                              <option value="16">16                              <option value="17">17                              <option value="18">18                              <option value="19">19                              <option value="20">20                           </select>                         </div>                     </div>                 </div>                 <div class="col-xs-6">                     <div class="option_cont">                         <p class="heading_option">number of problems</p>                         <div class="options">                           <select id="num_problems_select">                              <option>10                              <option>20                              <option>25                              <option>50                              <option selected>100                           </select>                         </div>                     </div>                 </div>             </div>             <div class="row">                 <div class="col-xs-12">                     <div class="restart_cont">                         <input type="submit" class="restart" value="restart" />                     </div>                 </div>             </div>         </div>     </div> </div>  <div class="themebackgroundcolor footer">     <hr>     <center>         <a href="/info/about.html" target="_top">about</a> | <a             href="/info/sponsor.html" target="_top">sponsors</a> | <a             href="/info/privacy_policy.html" target="_top">privacy 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you have in total 3 columns. instead of using col-md-6 can divide col-md-4 = 12 grid. should solve problem take @ image preview. http://snag.gy/zgi7a.jpg