ul {
  height: 100px;
  display: flex;
  flex-direction: column;
  flex-wrap: wrap;
}
 <ul>
  <li><details><summary>        2001 </summary>
 Introduce namelist<br>
 <tt><font size=+1>    
  &nlm
 </tt></font><br><br>  
 Law Modified
 <tt><font size=+1>    
<br> law=2001,
 </tt></font><br><br>  
 Zero Bracket Amount
 <tt><font size=+1>    
<br> zbrack=4550,
7600,
6650,
 </tt></font><br><br>  
 Personal Exemption
 <tt><font size=+1>    
<br> exemp=2900,
 </tt></font><br><br>  
 XYZ Tables
 <tt><font size=+1>    <xmp>
  brackets=
       0,  22000,  89450, 190750, 364200, 462500, 693750,1.0E+29,
       0,  15700,  59850,  95350, 182100, 231250, 578125,1.0E+29,
       0,  11000,  44725,  95375, 182100, 231250, 578125,1.0E+29,
  rates=
 .000,.100,.120,.220,.240,.320,.350,.370,
 .000,.100,.120,.220,.240,.320,.350,.370,
 .000,.100,.120,.220,.240,.320,.350,.370,
 </xmp></tt></font><br><br>  
 EITC
 <tt><font size=+1>    
 <br>dy=2450,
 <br>crmax= 364,2428,4008,4008, 364,2428,4008,4008,
 <br>ymax= 5950,13090,13090,13090, 5950,13090,13090,13090,
 <br>rtbase=.076,.340,.400,.400,
 <br>rtless=.076,.160,.211,.211,
 </tt></font><br><br>  
 Terminate Namelist<tt><font size=+1>    <br> /END</tt></font><br><br>  
 </details>
  <li><details><summary>        2002 </summary>
 Introduce namelist<br>
 <tt><font size=+1>    
  &nlm
 </tt></font><br><br>  
 Law Modified
 <tt><font size=+1>    
<br> law=2002,
 </tt></font><br><br>  
 Zero Bracket Amount
 <tt><font size=+1>    
<br> zbrack=4700,
7850,
6900,
 </tt></font><br><br>  
 Personal Exemption
 <tt><font size=+1>    
<br> exemp=3000,
 </tt></font><br><br>  
 XYZ Tables
 <tt><font size=+1>    <xmp>
  brackets=
       0,  22000,  89450, 190750, 364200, 462500, 693750,1.0E+29,
       0,  15700,  59850,  95350, 182100, 231250, 578125,1.0E+29,
       0,  11000,  44725,  95375, 182100, 231250, 578125,1.0E+29,
  rates=
 .000,.100,.120,.220,.240,.320,.350,.370,
 .000,.100,.120,.220,.240,.320,.350,.370,
 .000,.100,.120,.220,.240,.320,.350,.370,
 </xmp></tt></font><br><br>  
 EITC
 <tt><font size=+1>    
 <br>dy=2550,
 <br>crmax= 376,2506,4140,4140, 376,2506,4140,4140,
 <br>ymax= 6050,13520,13520,13520, 7050,14520,14520,14520,
 <br>rtbase=.076,.340,.400,.400,
 <br>rtless=.076,.160,.211,.211,
 </tt></font><br><br>  
 Terminate Namelist<tt><font size=+1>    <br> /END</tt></font><br><br>  
 </details>
 </ul>